Playing three-dimensional video games boosts stereo vision.

Playing two-dimensional video games has been shown to result in improvements in a range of visual and cognitive tasks, and these improvements appear to generalize widely1,2,3,4,5,6. Here we report that young adults with healthy vision, surprisingly, showed a dramatic improvement in stereo vision after playing three-dimensional, but not two-dimensional, video games for a relatively short period of time. Intriguingly, neither group showed any significant improvement in binocular contrast sensitivity. This dissociation suggests that the visual enhancement was specific to genuine stereoscopic processing, not indirectly resulting from enhanced contrast processing, and required engaging in a disparity cue-rich three-dimensional environment.

Conspicuity of staircase configuration: Effects of markings and contrast.

PURPOSE: To be able to walk safely up or down a staircase, we must be able to judge the configuration and slope of the staircase and our viewing position. Adding markings to the stairs might help form correct perceptions of the staircase geometry. In this study, we examined how visual judgements about staircase configuration are affected by different marking patterns. METHODS: Fifteen normally sighted young participants viewed computer-generated images of staircases as seen from the top landing of the stairs. Marking patterns included contrasting baseboard, transverse edge-stripes, longitudinal side-stripes, longitudinal stripes, diamond patterns, longitudinal stripes extended to landing and diamond patterns extended to landing. For comparison, we included the no-marking condition as a control. We tested several contrast levels of marking patterns (3.2%-50%), pitch lines of the staircases (shallow/medium/steep) and viewing positions (left/centre/right). The effect of the overall shape cue of the staircase on participants' performance was also evaluated. We measured participants' accuracies in judging whether the staircase was shallow, medium or steep, and whether the viewing position was located to the left, centre or right. RESULTS: Transverse edge-stripes markings yielded fewer underestimations of slope (9% [transverse] vs. 18% [others]) when compared with other markers. The presence of an overall shape cue helped both slope (67% [presence] vs. 51% [absence]) and viewing position judgements (79% [presence] vs. 62% [absence]). When the overall shape cue was present, only the transverse edge-stripes markings yielded a significant improvement in performance (compared with no-marking condition). When the cue was absent, performance was significantly better with markings with high and moderate contrasts. CONCLUSIONS: Adding marking patterns such as high-contrast transverse stripes to stairs may help enhance the visibility of the stairs and judgements of staircase geometry. This might be particularly useful for people with visual impairment or normally sighted individuals under compromised environmental conditions.

Oculomotor responses of the visual system to an artificial central scotoma may not represent genuine visuomotor adaptation.

Patients with central vision loss often adopt a location outside their scotoma as the new reference for vision, the preferred retinal locus (PRL). The development of a PRL is important not only for the rehabilitation of patients with central vision loss, but also helps us better understand how the brain adapts to the lack of visual input. Many investigators studied this question using a gaze-contingent display paradigm by imposing an artificial scotoma to simulate central vision loss for normally sighted subjects, with an important assumption that the "PRL" thus developed is the result of visuomotor adaptation, as is the case for people with a real scotoma. In this study, we tested the validity of this assumption. We used a gaze-contingent display combined with an artificial scotoma to first train normally sighted subjects to develop a "PRL" for saccade eye movements. Then, we compared the properties of saccades when the artificial scotoma was randomly turned off or on. When the artificial scotoma was absent, subjects automatically reverted to using their fovea, with a shorter saccade latency. Our findings suggest that the development of a "PRL" in response to an artificial scotoma may represent a strategy, instead of a genuine visuomotor adaptation.

Spatial and temporal proximity of objects for maximal crowding.

Crowding refers to the deleterious visual interaction among nearby objects. Does maximal crowding occur when objects are closest to one another in space and time? We examined how crowding depends on the spatial and temporal proximity, retinally and perceptually, between a target and flankers. Our target was a briefly flashed T-stimulus presented at 10° right of fixation (3-o'clock position). It appeared at different target-onset-to-flanker asynchronies with respect to the instant when a pair of flanking Ts, revolving around the fixation target, reached the 3-o'clock position. Observers judged the orientation of the target-T (the crowding task), or its position relative to the revolving flankers (the flash-lag task). Performance was also measured in the absence of flanker motion: target and flankers were either presented simultaneously (closest retinal temporal proximity) with different angular spatial offsets, or were presented collinearly (closest retinal spatial proximity) with different temporal onset asynchronies. We found that neither retinal nor perceptual spatial or temporal proximity could account for when maximal crowding occurred. Simulations using a model based on feed-forward interactions between sustained and transient channels in static and motion pathways, taking into account the differential response latencies, can explain the crowding functions observed under various spatio-temporal conditions between the target and flankers.

The generality of the critical spacing for crowded optotypes: From Bouma to the 21st century.

It is rare to find a crowding manuscript that fails to mention "Bouma's law," the rule of thumb stating that flankers within a distance of about one half of the target eccentricity will induce crowding. Here we investigate the generality of this rule (even for just optotypes), the factors that modulate the critical spacing, and the evidence for the rule in Bouma's own data. We explore these questions by reanalyzing a variety of studies from the literature, running several new control experiments, and by utilizing a model that unifies flanked identification measurements between psychophysical paradigms. Specifically, with minimal assumptions (equivalent psychometric slopes across conditions, for example), crowded acuity can be predicted for arbitrary target sizes and flanker spacings, revealing a performance "landscape" that delineates the critical spacing. Last, we present a compact quantitative summary of the effects of different types of stimulus manipulations on optotype crowding.

Training to improve temporal processing of letters benefits reading speed for people with central vision loss.

Reading is slow and difficult for many people with central vision loss. A previous study showed that the temporal threshold for letter recognition is a major factor limiting reading speed for people with central vision loss. Here, we asked whether the temporal threshold for letter recognition for people with central vision loss could be improved through training and, if so, whether that would benefit reading. Training consisted of six sessions (3000 trials) of recognizing letter trigrams presented at fixation. Trigrams were initially presented at a baseline temporal threshold that was decreased by 0.1 log step when observers' letter recognition accuracies reached 80% or higher for four consecutive blocks. Before and after training, we measured observers' visual acuity, preferred retinal locus for fixation, fixation stability, reading speeds using the rapid serial visual presentation (RSVP) paradigm, the MNREAD Acuity Chart and 100-word passages, the baseline temporal threshold for letter recognition at 80% accuracy, and a visual-span profile. After training, the temporal threshold was decreased by 68%. This improvement was accompanied by a higher RSVP maximum reading speed (but no change in MNREAD and passage reading speeds) and a larger visual span. A mediation analysis showed that the relationship between the temporal threshold and RSVP maximum reading speed was mainly mediated by the information transfer rate (size of visual span/temporal duration). Our results showed that the temporal threshold for letter recognition is amenable to training and can improve RSVP reading speeds, offering a practical means to improve reading speed for people with central vision loss.

The Effect of Perceptual Learning on Face Recognition in Individuals with Central Vision Loss.

Purpose: To examine whether perceptual learning can improve face discrimination and recognition in older adults with central vision loss. Methods: Ten participants with age-related macular degeneration (ARMD) received 5 days of training on a face discrimination task (mean age, 78 ± 10 years). We measured the magnitude of improvements (i.e., a reduction in threshold size at which faces were able to be discriminated) and whether they generalized to an untrained face recognition task. Measurements of visual acuity, fixation stability, and preferred retinal locus were taken before and after training to contextualize learning-related effects. The performance of the ARMD training group was compared to nine untrained age-matched controls (8 = ARMD, 1 = juvenile macular degeneration; mean age, 77 ± 10 years). Results: Perceptual learning on the face discrimination task reduced the threshold size for face discrimination performance in the trained group, with a mean change (SD) of -32.7% (+15.9%). The threshold for performance on the face recognition task was also reduced, with a mean change (SD) of -22.4% (+2.31%). These changes were independent of changes in visual acuity, fixation stability, or preferred retinal locus. Untrained participants showed no statistically significant reduction in threshold size for face discrimination, with a mean change (SD) of -8.3% (+10.1%), or face recognition, with a mean change (SD) of +2.36% (-5.12%). Conclusions: This study shows that face discrimination and recognition can be reliably improved in ARMD using perceptual learning. The benefits point to considerable perceptual plasticity in higher-level cortical areas involved in face-processing. This novel finding highlights that a key visual difficulty in those suffering from ARMD is readily amenable to rehabilitation.

Sequential perceptual learning of letter identification and "uncrowding" in normal peripheral vision: Effects of task, training order, and cholinergic enhancement.

Human adults with normal vision are capable of improving performance on visual tasks through repeated practice. Previous work has shown that enhancing synaptic levels of acetylcholine (ACh) in healthy human adults with donepezil (trade name: Aricept) can increase the magnitude and specificity of perceptual learning (PL) for motion direction discrimination in the perifovea. In the current study, we ask whether increasing the synaptic levels of ACh in healthy human adults with donepezil boosts learning of low-contrast isolated letter identification and high-contrast flanked letter identification in normal peripheral vision. Two groups of observers performed sequential training over multiple days while ingesting donepezil. One group trained on isolated low-contrast letters in Phase 1 and crowded high-contrast letters in Phase 2, and the other group performed the reverse sequence, thereby enabling us to differentiate possible effects of drug and training order on PL of letter identification. All testing and training were performed monocularly in peripheral vision, at an eccentricity of 10 degrees along the lower vertical meridian. Our experimental design allowed us to evaluate the effects of sequential training and to ask whether increasing cholinergic signaling boosted learning and/or transfer of low-contrast isolated letter identification and high-contrast flanked letter identification in normal peripheral vision. We found that both groups improved on each of the two tasks. However, our results revealed an effect of training task order on flanked letter identification: Observers who trained on isolated targets first showed rapid early improvement in flanked letter identification but little to no additional improvement after 30 training blocks, while observers who first trained with flanked letters improved gradually on flanked letter identification over the entire 100-block course of training. In addition, we found no effect of donepezil on PL of either isolated or flanked letter identification. In other words, donepezil neither boosted nor blocked learning to identify isolated low-contrast letters or learning to uncrowd in normal peripheral vision.

Exploration of the functional consequences of fixational eye movements in the absence of a fovea.

A recent theory posits that ocular drifts of fixational eye movements serve to reformat the visual input of natural images, so that the power of the input image is equalized across a range of spatial frequencies. This "spectral whitening" effect is postulated to improve the processing of high-spatial-frequency information and requires normal fixational eye movements. Given that people with macular disease exhibit abnormal fixational eye movements, do they also exhibit spectral whitening? To answer this question, we computed the power spectral density of movies of natural images translated in space and time according to the fixational eye movements (thus simulating the retinal input) of a group of observers with long-standing bilateral macular disease. Just as for people with normal vision, the power of the retinal input at low spatial frequencies was lower than that based on the 1/f2 relationship, demonstrating spectral whitening. However, the amount of whitening was much less for observers with macular disease when compared with age-matched controls with normal vision. A mediation analysis showed that the eccentricity of the preferred retinal locus adopted by these observers and the characteristics of ocular drifts are important factors limiting the amount of whitening. Finally, we did not find a normal aging effect on spectral whitening. Although these findings alone cannot form a causal link between macular disease and spectral properties of eye movements, they suggest novel potential means of modifying the characteristics of fixational eye movements, which may in turn improve functional vision for people with macular disease.

Reading in the presence of macular disease: a mini-review.

PURPOSE: Reading is vital to full participation in modern society. To millions of people suffering from macular disease that results in a central scotoma, reading is difficult and inefficient, rendering reading as the primary goal for most patients seeking low vision rehabilitation. The goals of this review paper are to summarize the dependence of reading speed on several key visual and typographical factors and the current methods or technologies for improving reading performance for people with macular disease. IMPORTANT FINDINGS: In general, reading speed for people with macular disease depends on print size, text contrast, size of the visual span, temporal processing of letters and oculomotor control. Attempts at improving reading speed by reducing the crowding effect between letters, words or lines; or optimizing properties of typeface such as the presence of serifs or stroke-width thickness proved to be futile, with any improvement being modest at best. Currently, the most promising method to improve reading speed for people with macular disease is training, including perceptual learning or oculomotor training. SUMMARY: The limitation on reading speed for people with macular disease is likely to be multi-factorial. Future studies should try to understand how different factors interact to limit reading speed, and whether different methods could be combined to produce a much greater benefit.

Music-reading expertise modulates the visual span for English letters but not Chinese characters.

Recent research has suggested that the visual span in stimulus identification can be enlarged through perceptual learning. Since both English and music reading involve left-to-right sequential symbol processing, music-reading experience may enhance symbol identification through perceptual learning particularly in the right visual field (RVF). In contrast, as Chinese can be read in all directions, and components of Chinese characters do not consistently form a left-right structure, this hypothesized RVF enhancement effect may be limited in Chinese character identification. To test these hypotheses, here we recruited musicians and nonmusicians who read Chinese as their first language (L1) and English as their second language (L2) to identify music notes, English letters, Chinese characters, and novel symbols (Tibetan letters) presented at different eccentricities and visual field locations on the screen while maintaining central fixation. We found that in English letter identification, significantly more musicians achieved above-chance performance in the center-RVF locations than nonmusicians. This effect was not observed in Chinese character or novel symbol identification. We also found that in music note identification, musicians outperformed nonmusicians in accuracy in the center-RVF condition, consistent with the RVF enhancement effect in the visual span observed in English-letter identification. These results suggest that the modulation of music-reading experience on the visual span for stimulus identification depends on the similarities in the perceptual processes involved.

Orientation Information in Encoding Facial Expressions for People With Central Vision Loss.

Purpose: Patients with central vision loss face daily challenges on performing various visual tasks. Categorizing facial expressions is one of the essential daily activities. The knowledge of what visual information is crucial for facial expression categorization is important to the understanding of the functional performance of these patients. Here we asked how the performance for categorizing facial expressions depends on the spatial information along different orientations for patients with central vision loss. Methods: Eight observers with central vision loss and five age-matched normally sighted observers categorized face images into four expressions: angry, fearful, happy, and sad. An orientation filter (bandwidth = 23°) was applied to restrict the spatial information within the face images, with the center of the filter ranged from horizontal (0°) to 150° in steps of 30°. Face images without filtering were also tested. Results: When the stimulus visibility was matched, observers with central vision loss categorized facial expressions just as well as their normally sighted counterparts, and showed similar confusion and bias patterns. For all four expressions, performance (normalized d'), uncorrelated with any of the observers' visual characteristics, peaked between -30° and 30° filter orientations and declined systematically as the filter orientation approached vertical (90°). Like normally sighted observers, observers with central vision loss also relied mainly on mouth and eye regions to categorize facial expressions. Conclusions: Similar to people with normal vision, people with central vision loss rely primarily on the spatial information around the horizontal orientation, in particular the regions around the mouth and eyes, for recognizing facial expressions.

Feature contingencies when reading letter strings.

Many models posit the use of distinctive spatial features to recognize letters of the alphabet, a fundamental component of reading. It has also been hypothesized that when letters are in close proximity, visual crowding may cause features to mislocalize between nearby letters, causing identification errors. Here, we took a data-driven approach to investigate these aspects of textual processing. Using data collected from subjects identifying each letter in thousands of lower-case letter trigrams presented in the peripheral visual field, we found characteristic error patterns in the results suggestive of the use of particular spatial features. Distinctive features were seldom entirely missed, and we found evidence for errors due to doubling, masking, and migration of features. Dependencies both amongst neighboring letters and in the responses revealed the contingent nature of processing letter strings, challenging the most basic models of reading that ignore either crowding or featural decomposition.

Bolder print does not increase reading speed in people with central vision loss.

Patients with central vision loss are often advised by low vision rehabilitation professionals to read bolder print to ameliorate their reading difficulties. Is boldface print really effective in improving reading performance for people with central vision loss? In this study, we evaluated how reading speed depends on the stroke-width of text in people with central vision loss. Ten participants with long-standing central vision loss read aloud single, short sentences presented on a computer monitor, one word at a time, using rapid serial visual presentation (RSVP). Reading speed was calculated based on the RSVP word exposure duration that yielded 80% of words read correctly. Text was rendered in Courier and at six boldness levels, defined as the width of the letter-strokes normalized to that of the standard Courier font: 0.27, 0.72, 1, 1.48, 1.89 and 3.04× the standard. Reading speed was measured for two print sizes - 0.8× and 1.4× the critical print size (the smallest print size that can be read at the maximum reading speed). For all participants and both print sizes, reading speeds were essentially the same for text with stroke-width boldness ranging from 0.72 to 1.89× the standard, and were significantly lower for the thinnest and the boldest print. Most importantly, reading speed was not higher for bolder print than for the standard one. Despite the clinical wisdom that patients with central vision loss might benefit from bolder print, print with stroke-widths larger than the standard does not significantly improve reading speed for participants with central vision loss.

Orientation information in encoding facial expressions.

Previous research showed that we use different regions of a face to categorize different facial expressions, e.g. mouth region for identifying happy faces; eyebrows, eyes and upper part of nose for identifying angry faces. These findings imply that the spatial information along or close to the horizontal orientation might be more useful than others for facial expression recognition. In this study, we examined how the performance for recognizing facial expression depends on the spatial information along different orientations, and whether the pixel-level differences in the face images could account for subjects' performance. Four facial expressions-angry, fearful, happy and sad-were tested. An orientation filter (bandwidth = 23°) was applied to restrict information within the face images, with the center of the filter ranged from 0° (horizontal) to 150° in steps of 30°. Accuracy for recognizing facial expression was measured for an unfiltered and the six filtered conditions. For all four facial expressions, recognition performance (normalized d') was virtually identical for filter orientations of -30°, horizontal and 30°, and declined systematically as the filter orientation approached vertical. The information contained in mouth and eye regions is a significant predictor for subject's response (based on the confusion patterns). We conclude that young adults with normal vision categorizes facial expression most effectively based on the spatial information around the horizontal orientation which captures primary changes of facial features across expressions. Across all spatial orientations, the information contained in mouth and eye regions contributes significantly to facial expression categorization.

Suboptimal eye movements for seeing fine details.

Human eyes are never stable, even during attempts of maintaining gaze on a visual target. Considering transient response characteristics of retinal ganglion cells, a certain amount of motion of the eyes is required to efficiently encode information and to prevent neural adaptation. However, excessive motion of the eyes leads to insufficient exposure to the stimuli, which creates blur and reduces visual acuity. Normal miniature eye movements fall in between these extremes, but it is unclear if they are optimally tuned for seeing fine spatial details. We used a state-of-the-art retinal imaging technique with eye tracking to address this question. We sought to determine the optimal gain (stimulus/eye motion ratio) that corresponds to maximum performance in an orientation-discrimination task performed at the fovea. We found that miniature eye movements are tuned but may not be optimal for seeing fine spatial details.

Visual Acuity Is Not the Best at the Preferred Retinal Locus in People with Macular Disease.

SIGNIFICANCE: Little is known about how the preferred retinal locus (PRL) develops in patients with macular disease. We found that acuity is worse at the PRL than at other retinal locations around the scotoma, suggesting that the selection of the PRL location is unlikely to be based on optimizing acuity. PURPOSE: Following the onset of bilateral macular disease, most patients adopt a retinal location outside the central scotoma, the PRL, as their new retinal location for visual tasks. Very little information is known about how the location of a PRL is chosen. In this study, we tested the hypothesis that the selection of the location for a PRL is based on optimizing visual acuity, which predicts that acuity is the best at the PRL, compared with other retinal locations. METHODS: Using a scanning laser ophthalmoscope that allowed us to position visual targets at precise retinal locations, we measured acuity psychophysically using a four-orientation Tumbling-E presented at the PRL and at multiple (ranged between 23 and 36 across observers) locations around the scotoma for five observers with bilateral macular disease. RESULTS: For all five observers, the acuity at the PRL was never the best among all testing locations. Instead, acuities were better at 15 to 86% of the testing locations other than the PRL, with the best acuity being 17 to 58% better than that at the PRL. The locations with better acuities did not cluster around the PRL and did not necessarily lie at the same distance from the fovea or the PRL. CONCLUSIONS: Our finding that acuity is worse at the PRL than at other locations around the scotoma implies that the selection of the PRL location is unlikely to be based on optimizing acuity.

Training peripheral vision to read: Boosting the speed of letter processing.

Central-field loss necessitates the use of peripheral vision which makes reading slow and difficult. Slower temporal processing of letter recognition has been shown to be a limiting factor in peripheral letter recognition and reading. Previous studies showed that perceptual learning can increase the number of letters recognized on each fixation and is accompanied by an increase in reading speed. We hypothesized that improvement in temporal processing speed underlies the observed training effects. Here, we proposed an adaptive training procedure to focus on boosting the speed of letter recognition, and investigated whether peripheral reading would be enhanced by this training method. Seven normally-sighted subjects were trained with four daily one-hour sessions of a letter recognition task at 10° in the lower visual field in a pre/post design. During training, we adjusted stimulus duration on a block by block basis to maintain task difficulty near a pre-defined level of 80% performance accuracy. Stimulus duration progressively decreased with training, indicative of faster letter recognition at the 80% criterion. Following training, reading speed measured using a rapid serial visual presentation showed a substantial improvement in the trained (lower) field (41%) and the untrained (upper) field (27%), similar to the improvements observed from the training with a fixed stimulus duration. Despite being no more effective than the previous training, the adaptive temporal training method may allow individualized training, and may have advantages for clinical populations.