Seeing and Perceiving
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Published By Brill

1878-4763, 1878-4755

2012 ◽  
Vol 25 (5) ◽  
pp. 397-398
Author(s):  
Susana T. L. Chung ◽  
Zhong-lin Lu
Keyword(s):  

2012 ◽  
Vol 25 (5) ◽  
pp. 425-447 ◽  
Author(s):  
Kristina M. Rand ◽  
Margaret R. Tarampi ◽  
Sarah H. Creem-Regehr ◽  
William B. Thompson

For low vision navigation, misperceiving the locations of hazards can have serious consequences. Potential sources of such misperceptions are hazards that are not visually associated with the ground plane, thus, depriving the viewer of important perspective cues for egocentric distance. In Experiment 1, we assessed absolute distance and size judgments to targets on stands under degraded vision conditions. Normally sighted observers wore blur goggles that severely reduced acuity and contrast, and viewed targets placed on either detectable or undetectable stands. Participants in the detectable stand condition demonstrated accurate distance judgments, whereas participants in the undetectable stand condition overestimated target distances. Similarly, the perceived size of targets in the undetectable stand condition was judged to be significantly larger than in the detectable stand condition, suggesting a perceptual coupling of size and distance in conditions of degraded vision. In Experiment 2, we investigated size and implied distance perception of targets elevated above a visible horizon for individuals in an induced state of degraded vision. When participants’ size judgments are inserted into the size–distance invariance hypothesis (SDIH) formula, distance to above-horizon objects increased compared to those below the horizon. Together, our results emphasize the importance of salient visible ground-contact information for accurate distance perception. The absence of this ground-contact information could be the source of perceptual errors leading to potential hazards for low vision individuals with severely degraded acuity and contrast sensitivity.


2012 ◽  
Vol 25 (5) ◽  
pp. 409-424 ◽  
Author(s):  
Renee Karas ◽  
Allison M. McKendrick

Perceptual analogues of centre–surround suppression have been applied as indirect measures of cortical inhibitory function in several clinical disorders. Two tasks have been used: a centre–surround contrast perception task and a motion direction discrimination task, where the stimulus size and contrast is varied to measure surround suppression effects. The tasks are markedly different, yet previous literature implies that both measures indirectly assess inhibitory function and that results will be complementary. This is not the case for age-related effects on surround suppression, however, as previous reports using the different measures are conflicting. Here we use a low-spatial frequency, drifting grating version of the centre–surround contrast perception task, and compare results to those obtained with the motion direction task in a single group of older observers. Older adults demonstrate significantly increased perceptual surround suppression of contrast for drifting, high contrast stimuli. Using the motion discrimination task, older observers showed similar amounts of surround suppression for the largest stimulus. This study confirms that visual surround suppression is altered by ageing. The complexity of neuronal systems involved in centre–surround interactions makes it unlikely that a single perceptual task will be sufficient to describe the effects of clinical disorders on surround suppression.


2012 ◽  
Vol 25 (5) ◽  
pp. 493-520 ◽  
Author(s):  
Seong Taek Jeon ◽  
Daphne Maurer ◽  
Terri L. Lewis

Amblyopia is a condition involving reduced acuity caused by abnormal visual input during a critical period beginning shortly after birth. Amblyopia is typically considered to be irreversible during adulthood. Here we provide the first demonstration that video game training can improve at least some aspects of the vision of adults with bilateral deprivation amblyopia caused by a history of bilateral congenital cataracts. Specifically, after 40 h of training over one month with an action video game, most patients showed improvement in one or both eyes on a wide variety of tasks including acuity, spatial contrast sensitivity, and sensitivity to global motion. As well, there was evidence of improvement in at least some patients for temporal contrast sensitivity, single letter acuity, crowding, and feature spacing in faces, but not for useful field of view. The results indicate that, long after the end of the critical period for damage, there is enough residual plasticity in the adult visual system to effect improvements, even in cases of deep amblyopia caused by early bilateral deprivation.


2012 ◽  
Vol 25 (5) ◽  
pp. 449-469 ◽  
Author(s):  
Eric Castet ◽  
Michael Crossland

Several definitions, measurements, and implicit meanings of ‘fixation stability’ have been used in clinical vision research, leading to some confusion. One definition concerns eye movements observed within fixations (i.e., within periods separated by saccades) when observing a point target: drift, microsaccades and physiological tremor all lead to some degree of within-fixation instability. A second definition relates to eye position during multiple fixations (and saccades) when patients fixate a point target. Increased between-fixation variability, combined with within-fixation instability, is known to be associated with poorer visual function in people with retinal disease such as age-related macular degeneration. In this review article, methods of eye stability measurement and quantification are summarised. Two common measures are described in detail: the bivariate contour ellipse area (BCEA) and the within-isolines area. The first measure assumes normality of the underlying positions distribution whereas the second does not. Each of these measures can be applied to two fundamentally different kinds of eye position data collected during a period of target observation. In the first case, mean positions of eye fixations are used to obtain an estimate of between-fixation variability. In the second case, often used in clinical vision research, eye position samples recorded by the eyetracker are used to obtain an estimate that confounds within- and between-fixation variability.We show that these two methods can produce significantly different values of eye stability, especially when reported as BCEA values. Statistical techniques for describing eye stability when the distribution of eye positions is multimodal and not normally distributed are also reviewed.


2012 ◽  
Vol 25 (5) ◽  
pp. 399-408 ◽  
Author(s):  
Jin Qian ◽  
Samuel A. Adeseye ◽  
Scott B. Stevenson ◽  
Saumil S. Patel ◽  
Harold E. Bedell

Purpose: Persons who wear monovision correction typically receive a clear image in one eye and a blurred image in the other eye. Although monovision is known to elevate the minimum stereoscopic threshold (Dmin), it is uncertain how it influences the largest binocular disparity for which the direction of depth can reliably be perceived (Dmax). In this study, we comparedDmaxfor stereo when one eye’s image is blurred toDmaxwhen both eyes’ images are either clear or blurred.Methods: The stimulus was a pair of vertically oriented, random-line patterns. To simulate monovision correction with +1.5 or +2.5 D defocus, the images of the line patterns presented to one eye were spatially low-pass filtered while the patterns presented to the other eye remained unfiltered.Results: Compared to binocular viewing without blur,Dminis elevated substantially more in the presence of monocular than binocular simulated blur.Dmaxis reduced in the presence of simulated monocular blur by between 13 and 44%, compared to when the images in both eyes are clear. In contrast, when the targets presented to both eyes are blurred equally,Dmaxeither is unchanged or increases slightly, compared to the values measured with no blur.Conclusion: In conjunction with the elevation ofDmin, the reduction ofDmaxwith monocular blur indicates that the range of useful stereoscopic depth perception is likely to be compressed in patients who wear monovision corrections.


2012 ◽  
Vol 25 (5) ◽  
pp. 471-492 ◽  
Author(s):  
Nicholas D. Smith ◽  
David P. Crabb ◽  
Fiona C. Glen ◽  
Robyn Burton ◽  
David F. Garway-Heath

This study tests the hypothesis that patients with bilateral glaucoma exhibit different eye movements compared to normally-sighted people when viewing computer displayed photographs of everyday scenes. Thirty glaucomatous patients and 30 age-related controls with normal vision viewed images on a computer monitor whilst eye movements were simultaneously recorded using an eye tracking system. The patients demonstrated a significant reduction in the average number of saccades compared to controls (; mean reduction of 7% (95% confidence interval (CI): 3–11%)). There was no difference in average saccade amplitude between groups but there was between-person variability in patients. The average elliptical region scanned by the patients by a bivariate contour ellipse area (BCEA) analysis, was more restricted compared to controls (; mean reduction of 23% (95% (CI): 11–35%)). A novel analysis mapping areas of interest in the images indicated a weak association between severity of functional deficit and a tendency to not view regions typically viewed by the controls. In conclusion, some eye movements in some patients with bilateral glaucomatous defects differ from normal-sighted people of a similar age when viewing images of everyday scenes, providing evidence for a potential new window for looking into the functional consequences of the disease.


2012 ◽  
Vol 25 (0) ◽  
pp. 200
Author(s):  
David J. Lewkowicz

Human infancy is a time of rapid neural and behavioral development and multisensory perceptual skills emerge during this time. Both animal and human early deprivation studies have shown that experience contributes critically to the development of multisensory perception. Unfortunately, Bodison because the human deprivation studies have only studied adult responsiveness, little is known about the more immediate effects of early experience on multisensory development. Consequently, we have embarked on a program of research to investigate how early experience affects the development of multisensory perception in human infants. To do so, we have focused on multisensory perceptual narrowing, an experience-dependent process where initially broad perceptual tuning is narrowed to match the infant’s native environment. In this talk, I first review our work demonstrating that multisensory narrowing characterizes infants’ response to non-native (i.e., monkey) faces and voices, that the initially broad tuning is present at birth, that narrowing also occurs in the audiovisual speech domain, and that multisensory narrowing is an evolutionarily novel process. In the second part of the talk, I present findings from our most recent studies indicating that experience has a seemingly paradoxical effect on infant response to audio–visual synchrony, that experience narrows infant response to amodal language and intonational prosody cues, and that experience interacts with developmental changes in selective attention during the first year of life resulting in dramatic developmental shifts in human infants’ selective attention to the eyes and mouth of their interlocutors’ talking faces.


2012 ◽  
Vol 25 (0) ◽  
pp. 222 ◽  
Author(s):  
Michael J. Proulx ◽  
Achille Pasqualotto ◽  
Shuichiro Taya

The topographic representation of space interacts with the mental representation of number. Evidence for such number–space relations have been reported in both synaesthetic and non-synaesthetic participants. Thus far most studies have only examined related effects in sighted participants. For example, the mental number line increases in magnitude from left to right in sighted individuals (Loetscher et al., 2008, Curr. Biol.). What is unclear is whether this association arises from innate mechanisms or requires visual experience early in life to develop in this way. Here we investigated the role of visual experience for the left to right spatial numerical association using a random number generation task in congenitally blind, late blind, and blindfolded sighted participants. Participants orally generated numbers randomly whilst turning their head to the left and right. Sighted participants generated smaller numbers when they turned their head to the left than to the right, consistent with past results. In contrast, congenitally blind participants generated smaller numbers when they turned their head to the right than to the left, exhibiting the opposite effect. The results of the late blind participants showed an intermediate profile between that of the sighted and congenitally blind participants. Visual experience early in life is therefore necessary for the development of the spatial numerical association of the mental number line.


2012 ◽  
Vol 25 (0) ◽  
pp. 188
Author(s):  
Helena Sgouramani ◽  
Chris Muller ◽  
Leon van Noorden ◽  
Marc Leman ◽  
Argiro Vatakis

We report two experiments aiming to define how experience and stimulus enactment affect multisensory temporal integration for ecologically-valid stimuli. In both experiments, a number of different dance steps were used as audiovisual displays at a range of stimulus onset asynchronies using the method of constant stimuli. Participants were either professional dancers or non-dancers. In Experiment 1, using a simultaneity judgment (SJ) task, we aimed at defining — for the first time — the temporal window of integration (TWI) for dancers and non-dancers and the role of experience in SJ performance. Preliminary results showed that dancers had smaller TWI in comparison to non-dancers for all stimuli tested, with higher complexity (participant rated) dance steps requiring larger auditory leads for both participant groups. In Experiment 2, we adapted a more embodied point of view by examining how enactment of the stimulus modulates the TWIs. Participants were presented with simple audiovisual dance steps that could be synchronous or asynchronous and were asked to synchronize with the audiovisual display by actually performing the step indicated. A motion capture system recorded their performance at a millisecond level of accuracy. Based on the optimal integration hypothesis, we are currently looking at the data in terms of which modality will be dominant, considering that dance is a spatially (visual) and temporally (audio) coordinated action. Any corrective adjustments, accelerations–decelerations, hesitations will be interpreted as indicators of the perception of ambiguity in comparison to their performance at the synchronous condition, thus, for the first time, an implicit SJ response will be measured.


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