The Influence of Ground Contact and Visible Horizon on Perception of Distance and Size under Severely Degraded Vision

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.

Age Related Changes to Perceptual Surround Suppression of Moving Stimuli

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.

The Effect of Video Game Training on the Vision of Adults with Bilateral Deprivation Amblyopia

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.

Dmax for Stereoscopic Depth Perception with Simulated Monovision Correction

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.

Eye Movements in Patients with Glaucoma When Viewing Images of Everyday Scenes

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.

Quantifying Eye Stability During a Fixation Task: A Review of Definitions and Methods

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.

Human sounds facilitates conscious processing of emotional faces

The interaction of audio–visual signals transferring information about the emotional state of others may play a significant role in social engagement. There is ample evidence that recognition of visual emotional information does not necessarily depend on conscious processing. However, little is known about how multisensory integration of affective signals relates to visual awareness. Previous research using masking experiments has shown relative independence of audio–visual integration on visual awareness. However, masking does not capture the dynamic nature of consciousness in which dynamic stimulus selection depends on a multitude of signals. Therefore, we presented neutral and happy faces in one eye and houses in the other resulting in perceptual rivalry between the two stimuli while at the same time we presented laughing, coughing or no sound. The participants were asked to report when they saw the faces, houses or their mixtures and were instructed to ignore the playback of sounds. When happy facial expressions were shown participants reported seeing fewer houses in comparison to when neutral expressions were shown. In addition, human sounds increase the viewing time of faces in comparison when there was no sound. Taken together, emotional expressions of the face affect which face is selected for visual awareness and at the same time, this is facilitated by human sounds.

The impact of imagery-evoking category labels on perceived variety

Does sensory imagery influence consumers’ perception of variety for a set of products? We tested this possibility across two studies in which participants received one of three alternate coffee menus where all the coffees were the same but the category labels were varied on how imagery-evocative they were. The less evocative labels (i) were more generic in nature (e.g., ‘Sweet’ or ‘Category A’), whereas the more evocative ones related either (ii) to the sensory experience of coffee (e.g., ‘Sweet Chocolate Flavor’ or ‘Smokey-Sweet Charred Dark Roast’) or (iii) to imagery related to where the coffee was grown (e.g., ‘Rich Volcanic Soil’ or ‘Dark Rich Volcanic Soil’). The labels relating to where the coffee was grown was included as a second control to show that merely increasing imagery does not increase perceived variety; it is increasing the sensory imagery relating to the items that does so. As expected, only category labels that evoked sensory imagery increased consumers’ perception of variety, whereas imagining where the coffee was grown did not enhance perception of variety. This finding extends recent research that shows that the type of sensory information included in an ad alters the perceptions of a product (Elder and Krishna, 2010) by illustrating that the inclusion of sensory information can also alter the perceived variety of a set of products. Thus, the inclusion of sensory information can be used flexibly to alter perceptions of both a single product and a set of choice alternatives.

Crossmodal correspondences between chemosensory stimuli and musical notes

We report a series of experiments investigating crossmodal correspondences between various food-related stimuli (water-based solutions, milk-based flavoured solutions, crisps, chocolate and odours) and sounds varying in pitch and played by four different types of musical instruments. Participants tasted or smelled stimuli before matching them to a musical note. Our results demonstrate that participants preferentially match certain stimuli to specific pitches and instrument types. Through participants’ ratings of the stimuli along a number of dimensions (e.g., pleasantness, complexity, familiarity or sweetness), we explore the psychological dimensions involved in these crossmodal correspondences, using principal components analysis (PCA). While pleasantness seems to play an important role in the choice of instrument associated with chemosensory stimuli, the pitch seems to also depend on the quality of the taste (bitter, salty, sour or sweet). The level at which such crossmodal correspondences might occur, as well as the potential applications of such results, will be discussed.