Sample records for afterimage

  1. 'Mixing in' afterimage colors

    NARCIS (Netherlands)

    Lier, R.J. van; Vergeer, M.L.T.; Anstis, S.


    Coloured stimuli may reveal different afterimage colours at the same retinal location, depending on surface contours presented after the image (Van Lier and Vergeer, 2007 Perception 36 200 - 201). Here we demonstrate that the filling-in of the afterimage colour depends on the colours that are presen

  2. Continuous flash suppression reduces negative afterimages. (United States)

    Tsuchiya, Naotsugu; Koch, Christof


    Illusions that produce perceptual suppression despite constant retinal input are used to manipulate visual consciousness. Here we report on a powerful variant of existing techniques, continuous flash suppression. Distinct images flashed successively at approximately 10 Hz into one eye reliably suppress an image presented to the other eye. The duration of perceptual suppression is at least ten times greater than that produced by binocular rivalry. Using this tool we show that the strength of the negative afterimage of an adaptor was reduced by half when it was perceptually suppressed by input from the other eye. The more completely the adaptor was suppressed, the more strongly the afterimage intensity was reduced. Paradoxically, trial-to-trial visibility of the adaptor did not correlate with the degree of reduction. Our results imply that formation of afterimages involves neuronal structures that access input from both eyes but that do not correspond directly to the neuronal correlates of perceptual awareness. PMID:15995700

  3. Luminance contours can gate afterimage colors and 'real' colors

    NARCIS (Netherlands)

    Anstis, S.; Vergeer, M.L.T.; Lier, R.J. van


    It has long been known that colored images may elicit afterimages in complementary colors. We have already shown (Van Lier, Vergeer, & Anstis, 2009) that one and the same adapting image may result in different afterimage colors, depending on the test contours presented after the colored image. The c

  4. Object knowledge changes visual appearance: semantic effects on color afterimages. (United States)

    Lupyan, Gary


    According to predictive coding models of perception, what we see is determined jointly by the current input and the priors established by previous experience, expectations, and other contextual factors. The same input can thus be perceived differently depending on the priors that are brought to bear during viewing. Here, I show that expected (diagnostic) colors are perceived more vividly than arbitrary or unexpected colors, particularly when color input is unreliable. Participants were tested on a version of the 'Spanish Castle Illusion' in which viewing a hue-inverted image renders a subsequently shown achromatic version of the image in vivid color. Adapting to objects with intrinsic colors (e.g., a pumpkin) led to stronger afterimages than adapting to arbitrarily colored objects (e.g., a pumpkin-colored car). Considerably stronger afterimages were also produced by scenes containing intrinsically colored elements (grass, sky) compared to scenes with arbitrarily colored objects (books). The differences between images with diagnostic and arbitrary colors disappeared when the association between the image and color priors was weakened by, e.g., presenting the image upside-down, consistent with the prediction that color appearance is being modulated by color knowledge. Visual inputs that conflict with prior knowledge appear to be phenomenologically discounted, but this discounting is moderated by input certainty, as shown by the final study which uses conventional images rather than afterimages. As input certainty is increased, unexpected colors can become easier to detect than expected ones, a result consistent with predictive-coding models. PMID:26386775

  5. Neural Correlates of an Auditory Afterimage in Primary Auditory Cortex


    Noreña, A. J.; Eggermont, J. J.


    The Zwicker tone (ZT) is defined as an auditory negative afterimage, perceived after the presentation of an appropriate inducer. Typically, a notched noise (NN) with a notch width of 1/2 octave induces a ZT with a pitch falling in the frequency range of the notch. The aim of the present study was to find potential neural correlates of the ZT in the primary auditory cortex of ketamine-anesthetized cats. Responses of multiunits were recorded simultaneously with two 8-electrode arrays during 1 s...

  6. Multisensory Tracking of Objects in Darkness: Capture of Positive Afterimages by the Tactile and Proprioceptive Senses.

    Directory of Open Access Journals (Sweden)

    Brian W Stone

    Full Text Available This paper reports on three experiments investigating the contribution of different sensory modalities to the tracking of objects moved in total darkness. Participants sitting in the dark were exposed to a brief, bright flash which reliably induced a positive visual afterimage of the scene so illuminated. If the participants subsequently move their hand in the darkness, the visual afterimage of that hand fades or disappears; this is presumably due to conflict between the illusory visual afterimage (of the hand in its original location and other information (e.g., proprioceptive from a general mechanism for tracking body parts. This afterimage disappearance effect also occurs for held objects which are moved in the dark, and some have argued that this represents a case of body schema extension, i.e. the rapid incorporation of held external objects into the body schema. We demonstrate that the phenomenon is not limited to held objects and occurs in conditions where incorporation into the body schema is unlikely. Instead, we propose that the disappearance of afterimages of objects moved in darkness comes from a general mechanism for object tracking which integrates input from multiple sensory systems. This mechanism need not be limited to tracking body parts, and thus we need not invoke body schema extension to explain the afterimage disappearance. In this series of experiments, we test whether auditory feedback of object movement can induce afterimage disappearance, demonstrate that the disappearance effect scales with the magnitude of proprioceptive feedback, and show that tactile feedback alone is sufficient for the effect. Together, these data demonstrate that the visual percept of a positive afterimage is constructed not just from visual input of the scene when light reaches the eyes, but in conjunction with input from multiple other senses.

  7. Visible light induced ocular delayed bioluminescence as a possible origin of negative afterimage

    CERN Document Server

    Bokkon, I; Wang, C; Dai, J; Salari, V; Grass, F; Antal, I


    The delayed luminescence of biological tissues is an ultraweak reemission of absorbed photons after exposure to external monochromatic or white light illumination. Recently, Wang, B\\'okkon, Dai and Antal (Brain Res. 2011) presented the first experimental proof of the existence of spontaneous ultraweak biophoton emission and visible light induced delayed ultraweak photon emission from in vitro freshly isolated rat's whole eye, lens, vitreous humor and retina. Here, we suggest that the photobiophysical source of negative afterimage can also occur within the eye by delayed bioluminescent photons. In other words, when we stare at a colored (or white) image for few seconds, external photons can induce excited electronic states within different parts of the eye that is followed by a delayed reemission of absorbed photons for several seconds. Finally, these reemitted photons can be absorbed by nonbleached photoreceptors that produce a negative afterimage. Although this suggests the photobiophysical source of negativ...

  8. Marcin Stańczyk’s Afterimages and Aftersounds – Reflections and Self-Reflections

    Directory of Open Access Journals (Sweden)

    Tabakiernik Marta


    Full Text Available One of the most frequently recurring topics in Marcin Stańczyk’s (b. 1977 self-commentaries is the idea of translating the phenomenon of afterimages into music, in the form of his original concept of aftersounds. Direct inspiration for this concept came from a cycle of solarist paintings by Władysław Strzemiński entitled Afterimages of the Sun. The concept of aftersounds can be considered on the level of music material (resonances and reflections of various kinds, contrasts on the sound level as well as metaphorically (when the composition becomes an afterimage of an external phenomenon. Particularly important to Stańczyk’s work as a composer are explorations in the field of music perception and the theatricalisation of performance, which turns every gesture of the performers into a meaningful element of the composition, as well as an element of expression. This paper aims to present an outline of the ways in which Stańczyk implements the idea of aftersounds in music. The text is based on the composer’s own statements as well as on characteristic examples from his works.

  9. Transformation of the Visual Afterimage Under Subject's Eye and Body Movements and the Visual Field Constancy Mechanisms. (United States)

    Zenkin, Gary M; Petrov, Alexander P


    Two types of positive afterimages differing in their structural complexity--called poor and rich--were used to investigate the visual field constancy mechanisms during eye and head movements. In the case of a poor afterimage, consistent with Emmert's law, every eye and head movement caused the afterimage to appear moving (in exactly the same way), unlike a real object, which appeared to remain stationary during those same eye and head movements (although its retinal image moved opposite to the eye movement). However, in the case of a rich afterimage, the afterimage appeared stationary during eye movements, while a small stationary test light in the real space appeared to move, violating Emmert's law. It is suggested that, in these two cases, the different apparent transformations reflected functioning of different constancy mechanisms. Both mechanisms implement projection of retinal images upon a hypothetical constant visual screen in strict accordance with the subject's movements but in two different ways. The experiments have indicated that, during binocular fusion, the visual afferent system is able to use information from the structural organization of the visual flow to implement the visual field stability and to calculate gaze direction independently of proprioceptive signals. PMID:26562912

  10. Observation of the effect of children amblyopia with virtual technology combined afterimage therapy%虚拟技术与后象联合治疗儿童弱视的疗效观察

    Institute of Scientific and Technical Information of China (English)



    Objective To discuss the curative effect of children amblyopia with virtual technology combined afterimage therapy. Methods The analysis was done from 2009. 10 to 2010. 12 for 91 amblyopic children( 163 eyes) who had been treated with virtual technology combined afterimage therapy in my hospital. Results The total effective rate of 163 eyes was 95.09% , in which 118 eyes (72. 39% ) were cured basically ,37 eyes (22. 70% ) were effective,37 eyes (4. 9% ) were ineffective. Conclusion (Dthe degree of amblyopia is lighter ,the effect is better;?The effect of centre watch children is better than that of those who watched beside the center;?The type of refractive error has the best effect in all types of amblyopia;@The treatment age of amblyopia is younger ,the effect is better. The therapy of virtual technology combined afterimage therapy has exact effect in children amblyopia.%目的 观察虚拟技术与后象联合治疗儿童弱视的疗效.方法 我院眼科2009年10月~2010年12月采用虚拟技术与后象联合治疗儿童弱视91例163眼.结果 163只眼总有效率为95.09%,其中基本治愈118眼(72.39%)有效37眼(22.70%),无效37眼(4.9%).结论 ①弱视程度越轻其疗效越好;②中心注视者的疗效较旁中心注视者疗效好;③各种类型弱视的疗效以屈光不正性最好;④弱视治疗年龄越小越好.虚拟技术与后象联合治疗儿童弱视效果确切.

  11. Efficacy of strengthened afterimage therapy of comprehensive treatment of 488 cases of children's amblyopia%强化后像综合疗法治疗儿童弱视488例观察

    Institute of Scientific and Technical Information of China (English)

    郑树锋; 李武军


    Objective To investigate the efficacy of strengthened afterimage therapy as comprehensive treatment in children's amblyopia. Methods A total of 488 cases diagnosed as visually impaired in 598 out-patient pediatric patients, according to the different causes of amblyopia, were given to strengthen afterimage therapy as the main comprehensive treatment for amblyopia age, amblyopia type, degree of amblyopia,amblyopia the nature of the as well as the efficacy of amblyopia treatment time and the relationship between the respective analysis. Results By strengthened afterimage therapy as the main comprehensive treatment, followed-up of 1-2 years, 488 cases of 598 eyes: Basic cured 378, valid 170 and invalid 50. The total effective treatment of amblyopia 91.64%, of which 63.21% cure rate, progressive 28.43%, invalid 8.36%, 3-6 year age group, ametropia amblyopia, mild amblyopia, central monitor the treatment of the highest cure rate, treatment time, adhere to the longer the treatment the better. Conclusions The efficacy ofamblyopia and the children's age, the type of amblyopia, amblyopia nature, extent and amblyopia, amblyopia treatment time is closely related to, and strengthened afterimage therapy as comprehensive treatment with amblyopia therapy curative effect is significant, worthy to be popularized.%目的 探讨强化后像综合疗法治疗儿童弱视的疗效.方法 对确诊为弱视的488例598只眼门诊儿童患者,按不同原因引起的弱视,分别给予以强化后像为主的综合治疗,对弱视的年龄、弱视的类型、弱视的程度、弱视的性质以及弱视治疗的时间与疗效的关系分别进行分析.结果 通过强化后 像为主的综合治疗,随访1-2年,488例598只眼:基本治愈378只眼,有效170只眼,无效50只眼.弱视治疗的总有效率91.64%,其中治愈率63.21%,进步28.43,无效8.36%,3~6岁年龄组、屈光不正性弱视、轻度弱视、中心性注视治疗治愈率最高,治疗时间坚持越

  12. Continuous flash suppression reduces negative afterimages


    Tsuchiya, Naotsugu; Koch, Christof


    Illusions that produce perceptual suppression despite constant retinal input are used to manipulate visual consciousness. Here we report on a powerful variant of existing techniques, continuous flash suppression. Distinct images flashed successively at approx10 Hz into one eye reliably suppress an image presented to the other eye. The duration of perceptual suppression is at least ten times greater than that produced by binocular rivalry. Using this tool we show that the strength of the negat...

  13. Opposing effects of attention and consciousness on afterimages


    van Boxtel, Jeroen J. A.; Tsuchiya, Naotsugu; Koch, Christof


    The brain's ability to handle sensory information is influenced by both selective attention and consciousness. There is no consensus on the exact relationship between these two processes and whether they are distinct. So far, no experiment has simultaneously manipulated both. We carried out a full factorial 2 × 2 study of the simultaneous influences of attention and consciousness (as assayed by visibility) on perception, correcting for possible concurrent changes in attention and consciousnes...

  14. 'Flight of colours' in lesions of the visual system. (United States)

    Feldman, M; Todman, L; Bender, M B


    A bright pocket flashlight was directed into one eye for 10 seconds; the subject then closed the eyelids and reported the sequence of after-image colours observed. Lesions of the visual system which compromised bilateral central colour vision also reduced or abolished the `flight of colours'. This simple bedside test of each eye independently is of value in detecting mild defects of central vision. PMID:4457619

  15. Mystery of the anti-McCollough effect. (United States)

    Bedford, Felice L


    The McCollough Effect (ME) is a complex perceptual aftereffect that remains of interest half a century after its discovery. It is argued that a recently reported variant, dubbed the anti-McCollough effect, is not the reverse of the ME, with aftereffect colors in the same direction as the inducing stimuli. A red-horizontal stimulus leads to a reddish aftereffect not because of red-horizontal parings, but despite them. The anti-ME is a weak standard-direction ME produced by complementary afterimage colors (afterimage green with horizontal), rather than by environmental colors, first shown decades ago. It is not a new type of contingent aftereffect. The red-horizontal pair does not interfere with the afterimage green-horizontal pair it produces because a single color-orientation pairing provides more ambiguous input than does the standard two orientation-color pairings (red-horizontal, green-vertical) of the ME. It is also argued that not even one orientation-contingent color aftereffect is convincingly shown in the "anti"-ME, let alone, as has previously been suggested, two simultaneous orientation-contingent color aftereffects in opposite directions at different levels of the visual system, in which the higher-level effect suppresses the downstream effect from reaching consciousness. The "anti"-ME can be explained by existing theories of contingent aftereffects, including perceptual-learning theory. PMID:21691903

  16. Disturbance of visual functions as a result of temporary blinding from low power lasers (United States)

    Reidenbach, Hans-Dieter


    Although it is well-known that dazzle, flash-blindness and afterimages may be caused by bright optical radiation, only sparse quantitative data are available with regard to the effects arising from low power laser products. Indirect effects like temporary blinding might result in serious incidents or even accidents due to the alteration of visual functions like visual acuity, contrast sensitivity and color discrimination. In order to determine the degree and duration of impairment resulting from dazzle, flash-blindness and afterimages, caused by a laser beam, an investigation has been performed with the goal to improve the current knowledge as far as especially the visual acuity recovery duration is concerned. Two different test set-ups were designed and applied in order to determine the afterimage duration and the recovery time for visual acuity after temporary blinding from a laser, respectively. In order to get the desired information a helium-neon laser was mounted on a movable assembly where the respective beam position and direction could be set up on a semicircle. In addition the mount could be inclined in a vertical plane in order to increase the variability of feasible settings. The power was adjusted in several steps in order to investigate the respective dependence of the afterimage. The investigations were relatively time consuming, since re-adaptation of about half an hour was necessary after every exposure in order not to falsify the results. The trials have been done with several volunteers in the laboratory. After the experimental mapping of the local afterimage duration for the various sites on the retina the foveal afterimage duration taf,fv produced by a red laser beam was determined. The investigations have shown a strong dependence on the angle between the line of sight and the beam direction. Besides a maximum of 300 s the dose relationship taf,fv/s ~ 50.6•ln[(P•texp)/μJ] - 13.4 for laser output powers P between 10 μW and 30 μW with

  17. How Were Eye Movements Recorded Before Yarbus? (United States)

    Wade, Nicholas J


    Alfred Yarbus introduced a new dimension of precision in recording how the eyes moved, either when attempts were made to keep them stationary or when scanning pictures. Movements of the eyes had been remarked upon for millennia, but recording how they move is a more recent preoccupation. Emphasis was initially placed on abnormalities of oculomotor function (like strabismus) before normal features were considered. The interest was in where the eyes moved to rather than determining how they got there. The most venerable technique for examining ocular stability involved comparing the relative motion between an afterimage and a real image. In the late 18th century, Wells compared afterimages generated before body rotation with real images observed following it when dizzy; he described both lateral and torsional nystagmus, thereby demonstrating the directional discontinuities in eye velocities. At around the same time Erasmus Darwin used afterimages as a means of demonstrating ocular instability when attempting to fixate steadily. However, the overriding concern in the 19th century was with eye position rather than eye movements. Thus, the characteristics of nystagmus were recorded before those of saccades and fixations. Eye movements during reading were described by Hering and by Lamare (working in Javal's laboratory) in 1879; both used similar techniques of listening (with tubes placed over the eyelids) to the sounds made during contractions of the extraocular muscles. Photographic records of eye movements during reading were made by Dodge early in the 20th century, and this stimulated research using a wider array of patterns. Eye movements over pictures were examined by Stratton and later by Buswell, who drew attention to the effects of instructions on the pattern of eye movements. In midcentury, attention shifted back to the stability of the eyes during fixation, with the emphasis on involuntary movements. The suction cap methods developed by Yarbus were applied

  18. Low energy He-Ne laser combined with the synthetic treatment amblyopia instrument in treating on eccentric fixation amblyopia%氦氖激光联合综合治疗仪治疗偏心注视性弱视

    Institute of Scientific and Technical Information of China (English)

    潘冰心; 楼倚天; 周武英; 莫萍萍


    目的 探讨氦氖激光联合后像法及广州视加弱视治疗仪治疗偏心注视性弱视的疗效分析.方法 对34例(56只眼)偏心注视弱视儿童进行氦氖激光联合后像法及广州视加弱视治疗仪治疗,其中男14例, 女20例,单眼弱视12例,其余22例为双眼弱视.年龄5~12岁,平均(8.18±1.85)岁.结果 34例(56只眼)弱视患者经第一疗程治疗后的治愈率为55.36%,第二疗程治疗后的治愈率为75.00%,第三疗程的治愈率达87.50%.结论 用氦氖激光联合后像法、广州视加弱视治疗仪治疗偏心注视性弱视的疗效肯定.较后像法联合遮盖,少数加用红色滤光片及光刷疗法(基本治愈率为37.72%),以及遮盖、增视疗法联合CAM疗法(基本治愈率为34.78%)治愈率提高,疗程缩短.%Objective To study the effects of the low energy He-Ne laser combined with the afterimage, synthetic treatment amblyopia instrument in treating on eccentric fixation amblyopia.Methods Thirty-four cases (56 eyes) with eccentric fixation amblyopia were treated with He-Ne laser,afterimage and synthetic treatment amblyopia instrument of Guang Zhou Shi Jia. Results The effect of the first in treatment was 55.36%,the effect of the second in treatment was 75.00%,and the third in treatment was 87.50%. Conclusions The effects of the low energy He-Ne laser combined with the afterimage,synthetic treatment amblyopia instrument of Guang Zhou Shi Jia in treating on eccentric fixation amblyopia is better than the effects of the afterimage,synthetic treatment amblyopia instrument.

  19. The Darwins and Wells: from revolution to evolution. (United States)

    Wade, Nicholas J


    In the biography of his grandfather (Erasmus Darwin), Charles Darwin hinted that his father (Robert Darwin) had received parental assistance in conducting and writing his medical thesis (which concerned afterimages). The experiments also involved visual vertigo, and they were elaborated by the senior Darwin in his Zoonomia, published in 1794. Erasmus Darwin's interpretation was in terms of trying to pursue peripheral afterimages formed during rotation; it was at variance with one published two years earlier by William Charles Wells, who had investigated the visual consequences of body rotation when the body is subsequently still. Wells penned two retorts to the Darwins' theory; although they were not accepted by Erasmus, he did devise a human centrifuge, models of which were employed in later studies of vertigo. Wells's ideas on evolution were expressed in a paper delivered to the Royal Society (in 1813) but not published in its Transactions. Commenting on the case of a white woman, part of whose skin was black, he proposed a process of change that was akin to natural selection. His ideas were acknowledged by Charles Darwin in the fourth edition of On the Origin of Species.

  20. A model for visual image-background discrimination by relative movement

    Institute of Scientific and Technical Information of China (English)

    陆惠民; 王秀春; 刘守忠; 史美德; 刘芳; 郭爱克


    Biologically plausible electronic neural network setup for real time processing motion image informa-tion was built. Using this setup the first part of the model was examined and real time discrimination of moving object image was realized from complex background in high resolution. Afterimages may play an important role in filtering moving object image and the aperture problem should be separated into two parts: the first part, i.e. the incomplete filtered moving object image, can be better resolved by parallel integration of multi-channel visual information, howev-er, the second part, i.e. the inaccurate measurement results for movement direction, may only get certain compensa-tion by visual integration.

  1. Mapping Collected Memory: An Exploration of Memory-Based Navigation in Amman, Jordan

    Directory of Open Access Journals (Sweden)

    Regina Mamou


    Full Text Available The purpose of this research is to explore navigational and image-making methods in a context where maps and formal address systems have been minimally consulted in recent years. This investigation is approached by way of a research-based art project on subjective cartography, which was carried out from 2009 to 2010 during a Fulbright fellowship to Amman, Jordan. The project examines the mutability of a specific location as well as its relationship between obsolescence in cartographic resources and the photographic medium. By reaching out to Ammani residents for informal tours of the city, selected guides were asked to narrate their experiences of navigating the city by memory and then directed to point out key landmarks during this process. Later, these tours were re-memorized and landmarks were photographed as a representation of the afterimage to capture high-quality still images through the use of a large-format photographic device. These afterimages are not intended to serve as documents or memorials of Amman but rather as ruminations on the faculties of memory in an ever-changing environment. This subjective experience, or the observation of a city’s minutiae amid wayfinding, poses a series of inquiries, vis-à-vis memory-based navigation and the role of still images, as an alternative to the panoptic view of a map. The result is a meditative project considering the plasticity of an urban entity, presented as a composition of written material and large-scale photographs, fragments of the city that when viewed as a series come together as a constellation of a subjective whole. 

  2. Follow-up of hearing thresholds among forge hammering workers

    Energy Technology Data Exchange (ETDEWEB)

    Kamal, A.A.; Mikael, R.A.; Faris, R. (Ain Shams Univ., Abbasia, Cairo (Egypt))


    Hearing threshold was reexamined in a group of forge hammering workers investigated 8 years ago with consideration of the age effect and of auditory symptoms. Workers were exposed to impact noise that ranged from 112 to 139 dB(A)--at an irregular rate of 20 to 50 drop/minute--and a continuous background noise that ranged from 90 to 94 dB(A). Similar to what was observed 8 years ago, the present permanent threshold shift (PTS) showed a maximum notch at the frequency of 6 kHz and considerable elevations at the frequencies of 0.25-1 kHz. The age-corrected PTS and the postexposure hearing threshold were significantly higher than the corresponding previous values at the frequencies 0.25, 0.5, 1, and 8 kHz only. The rise was more evident at the low than at the high frequencies. Temporary threshold shift (TTS) values were significantly less than those 8 years ago. Contrary to the previous TTS, the present TTS were higher at low than at high frequencies. Although progression of PTS at the frequencies 0.25 and 0.5 kHz was continuous throughout the observed durations of exposure, progression at higher frequencies occurred essentially in the first 10 to 15 years of exposure. Thereafter, it followed a much slower rate. Tinnitus was significantly associated with difficulty in hearing the human voice and with elevation of PTS at all the tested frequencies, while acoustic after-image was significantly associated with increment of PTS at the frequencies 0.25-2 kHz. No relation between PTS and smoking was found. PTS at low frequencies may provide an indication of progression of hearing damage when the sensitivity at 6 and 4 kHz diminishes after prolonged years of exposure. Tinnitus and acoustic after-image are related to the auditory effect of forge hammering noise.

  3. Apparent rotation and jazzing in Leviant's Enigma illusion. (United States)

    Hamburger, Kai


    In 1981 Leviant devised Enigma, a figure that elicits perceived rotary motion in the absence of real motion. However, despite its striking appearance there is no good explanation for this motion illusion to date. Gregory (1993 Proceedings of the Royal Society of London B 253 123) pointed out a similarity to MacKay's 'complementary' afterimage in his ray pattern and suggested accommodative fluctuations and small eye movements as a potential origin for these phenomena. Furthermore, Zeki et al (1993 Proceedings of the Royal Society of London B 252 215-222) found PET-activation in response to Enigma in visual area V5 and immediately surrounding areas (called V5 complex) suggesting that the illusory motion could be mediated by the same neurons as real motion. In the experiments reported here, I show that the rotary motion is perceived on coloured as well as achromatic annuli intercepting the radial lines. More importantly, the illusory streaming motion continues to be seen with a cycloplegic lens as well as through a pinhole (ie ruling out transient changes of accommodation), and in the positive after-image (ie in the absence of eye movements). Apparent rotation is strongest with radial inducers impinging at right angles onto the annuli, but persist, although to a lesser degree, when the inducing lines are tilted in opposite directions, non-collinear, or replaced by dotted lines or lines with rounded terminators. For an explanation, the Enigma illusion requires a neural mechanism that uses lines abutting an empty annulus to elicit orthogonal streaming motion in one or the other direction. PMID:17718359

  4. Are there multiple visual short-term memory stores?

    Directory of Open Access Journals (Sweden)

    Ilja G Sligte

    Full Text Available BACKGROUND: Classic work on visual short-term memory (VSTM suggests that people store a limited amount of items for subsequent report. However, when human observers are cued to shift attention to one item in VSTM during retention, it seems as if there is a much larger representation, which keeps additional items in a more fragile VSTM store. Thus far, it is not clear whether the capacity of this fragile VSTM store indeed exceeds the traditional capacity limits of VSTM. The current experiments address this issue and explore the capacity, stability, and duration of fragile VSTM representations. METHODOLOGY/PRINCIPAL FINDINGS: We presented cues in a change-detection task either just after off-set of the memory array (iconic-cue, 1,000 ms after off-set of the memory array (retro-cue or after on-set of the probe array (post-cue. We observed three stages in visual information processing 1 iconic memory with unlimited capacity, 2 a four seconds lasting fragile VSTM store with a capacity that is at least a factor of two higher than 3 the robust and capacity-limited form of VSTM. Iconic memory seemed to depend on the strength of the positive after-image resulting from the memory display and was virtually absent under conditions of isoluminance or when intervening light masks were presented. This suggests that iconic memory is driven by prolonged retinal activation beyond stimulus duration. Fragile VSTM representations were not affected by light masks, but were completely overwritten by irrelevant pattern masks that spatially overlapped the memory array. CONCLUSIONS/SIGNIFICANCE: We find that immediately after a stimulus has disappeared from view, subjects can still access information from iconic memory because they can see an after-image of the display. After that period, human observers can still access a substantial, but somewhat more limited amount of information from a high-capacity, but fragile VSTM that is overwritten when new items are presented

  5. True Detective Stories: Media Textuality and the Anthology Format between Remediation and Transmedia Narratives

    Directory of Open Access Journals (Sweden)

    Cristina Demaria


    Full Text Available Through the analysis of the recent HBO first season TV series True Detective (2014-, the essays focuses on the renewed anthology format of contemporary seriality as a way to inscribe the form of the novel in the transmedia imagination and its narrative models. While the first part of the essay concentrates on Media and Literary Studies’ debates on the statute of media texts, their materiality and the transformations of their contents in the participatory and convergent culture of prosumers, the second part is devoted to an in-depth reading of some of the main features of True Detective’s first season: from the ways it remediates many other genres and media, to how – as an audiovisual sychretyc text -  it plays with dialogues, cinematography, music and its temporal, spatial and seeing enunciative strategies and positions in order to construct a (quasidystopic narrative of America as an after-image, or, better, a post-collapse America and its Southern Gothic landscapes. In the lst paragraph, this writing briefly engages with how this particular format of TV series helps developing narrative models that fan we bpages and fanfic archives are still struggling not so much to comprehend, but to actually transform into an expanded textuality  able to tell a more ‘true’ story.

  6. Robust Foreground Detection: A Fusion of Masked GreyWorld, Probabilistic Gradient Information and Extended Conditional Random Field Approach

    Directory of Open Access Journals (Sweden)

    David Rawlinson


    Full Text Available Foreground detection has been used extensively in many applications such as people counting, traffic monitoring and face recognition. However, most of the existing detectors can only work under limited conditions. This happens because of the inability of the detector to distinguish foreground and background pixels, especially in complex situations. Our aim is to improve the robustness of foreground detection under sudden and gradual illumination change, colour similarity issue, moving background and shadow noise. Since it is hard to achieve robustness using a single model, we have combined several methods into an integrated system. The masked grey world algorithm is introduced to handle sudden illumination change. Colour co-occurrence modelling is then fused with the probabilistic edge-based background modelling. Colour co-occurrence modelling is good infiltering moving background and robust to gradual illumination change, while an edge-based modelling is used for solving a colour similarity problem. Finally, an extended conditional random field approach is used to filter out shadow and afterimage noise. Simulation results show that our algorithm performs better compared to the existing methods, which makes it suitable for higher-level applications.

  7. Hazards in air-, rail-, and road traffic arising from laserpointers; Gefaehrdungen des Luft-, Schienen- und Strassenverkehrs durch Laserpointer

    Energy Technology Data Exchange (ETDEWEB)

    Reidenbach, H.D. [Fachhochschule Koeln (Germany). Forschungsschwerpunkt Medizintechnik und Nichtionisierende Strahlung; Deutsch-Schweizerischer Fachverband fuer Strahlenschutz e.V., Garching (Germany). Arbeitskreis Nichtionisierende Strahlung (AKNIR)


    Visible laser radiation with sufficient irradiance or radiant exposure might result in permanent damage of the eyes especially in the retina. In order to prevent this exposure limit values have been established based on current scientific knowledge. In addition visible laser radiation might result in effects like temporary blinding at even much lower exposure values. In this case irritations, flash-blindness and afterimages appear whose extent might exceed the respective damage level while vision is temporarily compromised in critical visual tasks more or less. The easy accessibility of hand-held laser products (laser pointers) with relatively high power might result in a modification of the security situation especially in air traffic via thoughtless and careless use of such products or in terroristic acts. In addition an increasing number of incidents in rail and road traffic where not only temporary blinding might be anticipated but permanent damage of the eyes as a result of overexposure due to laser pointer irradiation cannot be excluded any longer. Using laser pointers, which are available on the market in the power range up to 1 watt and at different wavelengths new hazard scenarios and threats with serious consequences are possible. Here the radiation protection is in great demand. (orig.)

  8. Adjusting to a sudden “aging” of the lens. (United States)

    Tregillus, Katherine E M; Werner, John S; Webster, Michael A


    Color perception is known to remain largely stable across the lifespan despite the pronounced changes in sensitivity from factors such as the progressive brunescence of the lens. However, the mechanisms and timescales controlling these compensatory adjustments are still poorly understood. In a series of experiments, we tracked adaptation in observers after introducing a sudden change in lens density by having observers wear glasses with yellow filters that approximated the average spectral transmittance of a 70-year-old lens. Individuals were young adults and wore the glasses for 5 days for 8 h per day while engaged in their normal activities. Achromatic settings were measured on a CRT before and after each daily exposure with the lenses on and off, and were preceded by 5 min of dark adaptation to control for short-term chromatic adaptation. During each day, there was a large shift in the white settings consistent with a partial compensation for the added lens density. However, there was little to no evidence of an afterimage at the end of each daily session, and participants’ perceptual nulls were roughly aligned with the nulls for short-term chromatic adaptation, suggesting a rapid renormalization when the lenses were removed. The long-term drift was also extinguished by brief exposure to a white adapting field. The results point to distinct timescales and potentially distinct mechanisms compensating for changes in the chromatic sensitivity of the observer. PMID:26924924

  9. Removing the remaining ridges in fingerprint segmentation

    Institute of Scientific and Technical Information of China (English)

    ZHU En; ZHANG Jian-ming; YIN Jian-ping; ZHANG Guo-min; HU Chun-feng


    Fingerprint segmentation is an important step in fingerprint recognition and is usually aimed to identify non-ridge regions and unrecoverable low quality ridge regions and exclude them as background so as to reduce the time expenditure of image processing and avoid detecting false features. In high and in low quality ridge regions, often are some remaining ridges which are the afterimages of the previously scanned finger and are expected to be excluded from the foreground. However, existing segmentation methods generally do not take the case into consideration, and often, the remaining ridge regions are falsely classified as foreground by segmentation algorithm with spurious features produced erroneously including unrecoverable regions as foreground. This paper proposes two steps for fingerprint segmentation aimed at removing the remaining ridge region from the foreground. The non-ridge regions and unrecoverable low quality ridge regions are removed as background in the first step, and then the foreground produced by the first step is further analyzed for possible remove of the remaining ridge region. The proposed method proved effective in avoiding detecting false ridges and in improving minutiae detection.

  10. Evaporative respiratory cooling augments pit organ thermal detection in rattlesnakes. (United States)

    Cadena, Viviana; Andrade, Denis V; Bovo, Rafael P; Tattersall, Glenn J


    Rattlesnakes use their facial pit organs to sense external thermal fluctuations. A temperature decrease in the heat-sensing membrane of the pit organ has the potential to enhance heat flux between their endothermic prey and the thermal sensors, affect the optimal functioning of thermal sensors in the pit membrane and reduce the formation of thermal "afterimages", improving thermal detection. We examined the potential for respiratory cooling to improve strike behaviour, capture, and consumption of endothermic prey in the South American rattlesnake, as behavioural indicators of thermal detection. Snakes with a higher degree of rostral cooling were more accurate during the strike, attacking warmer regions of their prey, and relocated and consumed their prey faster. These findings reveal that by cooling their pit organs, rattlesnakes increase their ability to detect endothermic prey; disabling the pit organs caused these differences to disappear. Rattlesnakes also modify the degree of rostral cooling by altering their breathing pattern in response to biologically relevant stimuli, such as a mouse odour. Our findings reveal that low humidity increases their ability to detect endothermic prey, suggesting that habitat and ambush site selection in the wild may be influenced by external humidity levels as well as temperature.

  11. Hazards in air-, rail-, and road traffic arising from laserpointers

    International Nuclear Information System (INIS)

    Visible laser radiation with sufficient irradiance or radiant exposure might result in permanent damage of the eyes especially in the retina. In order to prevent this exposure limit values have been established based on current scientific knowledge. In addition visible laser radiation might result in effects like temporary blinding at even much lower exposure values. In this case irritations, flash-blindness and afterimages appear whose extent might exceed the respective damage level while vision is temporarily compromised in critical visual tasks more or less. The easy accessibility of hand-held laser products (laser pointers) with relatively high power might result in a modification of the security situation especially in air traffic via thoughtless and careless use of such products or in terroristic acts. In addition an increasing number of incidents in rail and road traffic where not only temporary blinding might be anticipated but permanent damage of the eyes as a result of overexposure due to laser pointer irradiation cannot be excluded any longer. Using laser pointers, which are available on the market in the power range up to 1 watt and at different wavelengths new hazard scenarios and threats with serious consequences are possible. Here the radiation protection is in great demand. (orig.)

  12. New methods in order to determine the extent of temporary blinding from laser and LED light and proposal how to allocate into blinding groups (United States)

    Reidenbach, Hans-Dieter; Ott, Günter; Brose, Martin; Dollinger, Klaus


    Indirect effects arising from bright artificial optical sources like temporary blinding might result in serious incidents or even accidents due to accompanying alteration of visual functions like visual acuity, contrast sensitivity and color discrimination. In order to determine the degree and duration of impairment resulting from glare, dazzle, flash-blindness and afterimages, caused by a beam from a laser or lamp product, particularly under low ambient light conditions, an investigation has been performed with the goal to improve the current knowledge as far as especially recovery duration of visual acuity is concerned. For this two different test set-ups were designed and engineered in order to be able to determine the time duration after which visual acuity returns to its previous value after temporary blinding with a laser or an LED and in addition to search for functional relations as far as wavelength, optical power and exposure duration are concerned. Instead of normal visual acuity measurement, which is the standard test done by eye care professionals, and which has been applied in order to determine the recovery time after irradiation with a high brightness LED (HB-LED) with the aid of a modified commercially available binoptometer with Landolt-C rings as optotypes, a special reading test on a computer monitor was developed for the case of laser irradiation. Two different laser were applied, one with a wavelength of 632.8 nm and the other with 532 nm. Red, green, royal blue and white HB-LEDs were used as stimulating light sources. The maximum applied optical power in a 7-mm aperture, which is equivalent to the pupil diameter of a dark adapted eye, was 0.783 mW (laser) and 3 mW (LED). The exposure durations were chosen as 0.25 s, 0.5 s, 1 s, 5 s, and 20 s in the case of laser irradiation and 0.25 s, 1 s, 5 s, and 10 s for LEDs, respecting maximum permissible exposure (MPE) and/or limit exposure levels (ELVs) in all exposure situations. The visual acuity

  13. Analysis of Multipath Pixels in SAR Images (United States)

    Zhao, J. W.; Wu, J. C.; Ding, X. L.; Zhang, L.; Hu, F. M.


    As the received radar signal is the sum of signal contributions overlaid in one single pixel regardless of the travel path, the multipath effect should be seriously tackled as the multiple bounce returns are added to direct scatter echoes which leads to ghost scatters. Most of the existing solution towards the multipath is to recover the signal propagation path. To facilitate the signal propagation simulation process, plenty of aspects such as sensor parameters, the geometry of the objects (shape, location, orientation, mutual position between adjacent buildings) and the physical parameters of the surface (roughness, correlation length, permittivity)which determine the strength of radar signal backscattered to the SAR sensor should be given in previous. However, it's not practical to obtain the highly detailed object model in unfamiliar area by field survey as it's a laborious work and time-consuming. In this paper, SAR imaging simulation based on RaySAR is conducted at first aiming at basic understanding of multipath effects and for further comparison. Besides of the pre-imaging simulation, the product of the after-imaging, which refers to radar images is also taken into consideration. Both Cosmo-SkyMed ascending and descending SAR images of Lupu Bridge in Shanghai are used for the experiment. As a result, the reflectivity map and signal distribution map of different bounce level are simulated and validated by 3D real model. The statistic indexes such as the phase stability, mean amplitude, amplitude dispersion, coherence and mean-sigma ratio in case of layover are analyzed with combination of the RaySAR output.

  14. Eye protection practices and symptoms among welders in the Limpopo Province of South Africa+

    Directory of Open Access Journals (Sweden)

    H. L. Sithole


    Full Text Available Welding is associated with several ocular and systemic hazards especially where adequate protective measures are not taken.  The purpose of this project was to study the eye protection practices and symptoms among welders in the Capricorn District of Limpopo Province, South Africa. Questionnaires designed to investigate eye protection practices and symptoms experienced were completed byone hundred and fifty (150 welders. The types of welding done were shielded metal arc (84%, oxyacetylene gas (4% and silver brazing (12%. The number of years spent in the welding industry ranged from one to 10 years with a mean of 5 ± 3.1 years and the number of hours of welding per day ranged from one to 10 hours with a mean of 6 ± 2.1 hours. A large percentage of the welders (89% reported wearing protective devices when welding and the most common protective devices used by the welders were: helmets (57%, goggles(22%, and face shields (15%. Six percent used inefficient protective devices such as sunglasses.  Sixty one percent reported occasional exposure to welding flashes when not wearing any eye protection. Welding-related eye symptoms reported included foreign body sensation (18%, persistent after-images (31%, and watery eyes (50%.  Al-though the majority of the welders wore protective devices while welding, a few did not always use such devices while others used sunglasses for protection.  Moreover, many of the welders were occasionally, and only a few were always, exposed to welding flashes when protective devices were not used. Therefore, we concluded that eye protectionpractices amongst the welders appeared to be inadequate to avoid hazards associated with welding.  It is recommended that an eye protection educational campaign for welders should form part of the SouthAfrican Government’s workplace safety program. 

  15. Efficacy of strengthened occlusion therapy combined comprehensive treatment in children with monocular am-blyopia%强化遮盖综合治疗儿童单眼弱视疗效分析

    Institute of Scientific and Technical Information of China (English)



    Objective To investigate the efficacy of strengthened occlusion therapy combined comprehensive treat-ment in children with monocular amblyopia. Methods A total of 216 cases out-patient pediatric patients (216 eyes) with monocular amblyopia,according to the different causes of amblyopia, were treated with strengthened occlusion therapy combined comprehensive treatment such as refractive correction,red filter treatment and afterimages.The treatment effect were observed for 12~36 months. Results In 216 eyes,the cure rate is 67.13%,progress is 28.70% and invalid is 4.17%. The younger amblyopia age,the better the treatment effect.The treatment effect was better for ametropia amblyopia, mild amblyopia, central gazing amblyopia. Conclusions The efficacy of amblyopia is closely related to the amblyopia age, type,gazing nature and degree. Strengthened occlusion therapy combined comprehensive treatment is efficiency.%目的:探讨强化遮盖综合疗法治疗儿童单眼弱视的疗效。方法对确诊为儿童单眼弱视的216例216眼门诊儿童患者,按弱视病因,分别给予以强化遮盖治疗为主,联合屈光矫正、红光闪烁、后像等综合治疗,随访观察12~36个月,分析其疗效。结果216例216眼,治愈率67.13%,进步28.70%,无效4.17%;初诊年龄越小,治疗效果越好;屈光不正性弱视、轻度弱视、中心注视性弱视治疗效果更好。结论弱视的疗效与患儿的年龄、弱视的类型、弱视的性质、弱视的程度密切相关,强化遮盖综合疗法治疗儿童单眼弱视疗效显著。

  16. 'Visual snow' - a disorder distinct from persistent migraine aura. (United States)

    Schankin, Christoph J; Maniyar, Farooq H; Digre, Kathleen B; Goadsby, Peter J


    Patients with 'visual snow' report continuous tiny dots in the entire visual field similar to the noise of an analogue television. As they frequently have migraine as a comorbidity with ophthalmological, neurological and radiological studies being normal, they are offered various diagnoses, including persistent migraine aura, post-hallucinogen flashback, or psychogenic disorder. Our aim was to study patients with 'visual snow' to characterize the phenotype. A three-step approach was followed: (i) a chart review of patients referred to us identified 22 patients with 'visual snow'. Fifteen had additional visual symptoms, and 20 patients had comorbid migraine, five with aura; (ii) to identify systematically additional visual symptoms, an internet survey (n = 275) of self-assessed 'visual snow' subjects done by Eye On Vision Foundation was analysed. In two random samples from 235 complete data sets, the same eight additional visual symptoms were present in >33% of patients: palinopsia (trailing and afterimages), entoptic phenomena (floaters, blue field entoptic phenomenon, spontaneous photopsia, self-light of the eye), photophobia, and nyctalopia (impaired night vision); and (iii) a prospective semi-structured telephone interview in a further 142 patients identified 78 (41 female) with confirmed 'visual snow' and normal ophthalmological exams. Of these, 72 had at least three of the additional visual symptoms from step (ii). One-quarter of patients had 'visual snow' as long as they could remember, whereas for the others the mean age of onset was 21 ± 9 years. Thirty-two patients had constant visual symptoms, whereas the remainder experienced either progressive or stepwise worsening. Headache was the most frequent symptom associated with the beginning or a worsening of the visual disturbance (36%), whereas migraine aura (seven patients) and consumption of illicit drugs (five, no hallucinogens) were rare. Migraine (59%), migraine with aura (27%), anxiety and depression

  17. 不同时距条件下面孔表情知觉的时间整合效应%Temporal Integration Effects in Facial Expression Recognition in Different Temporal Duration Condition

    Institute of Scientific and Technical Information of China (English)

    陈本友; 黄希庭


    通过把面孔表情分割成三部分,按照不同的时间间隔以及不同的呈现时间相继呈现,考察了被试对面孔表情的时间整合效果,以此探讨时间整合的加工过程和影响因素。结果发现:(1)面孔表情的时间整合效果受时间结构和刺激材料的影响。(2)分离呈现的面孔表情能否进行时间整合与S0A的大小有关。(3)面孔表情的时间整合存在类型差异。(4)面孔表情的时间整合是在一个有限的视觉缓冲器内进行的,图像记忆和长时记忆与面孔表情的时间整合过程关系密切。%Temporal integration is the process of perception processing,in which the successively separated stimuli are combined into a significant representation.It is a complicated process,which is known to be influenced by multiple factors,such as the temporal structure and stimulus components.Although this process has been explored in inter-stimulus interval in face perception,little is known about the temporal integration effect in facial expression recognition.More importantly,there has been no relevant evidence demonstrating that stimulus duration and stimulus category can affect the temporal integration of facial expression. In the present study,the part-whole judgment task was used to examine the influencing factors of temporal integration in the facial expression.In two experiments,each of three whole facial expression pictures was segmented into three parts,and each including a salient facial feature:eye,nose,or mouth.These parts were presented sequentially to the participants by some interval or presentation durations, with a fixed sequence:eye part first,nose followed,and mouth last.Following the last part,a mask,which eliminated effects of afterimages or other types of visual persistence was displayed.Then,participants were asked to judge the category of the facial expression, by pressing one of three number keys;"1","2" and "3",corresponding to anger,happy and