Gains following perceptual learning are closely linked to the initial visual acuity

Cognitive training with adaptive algorithm improves cognitive ability in older people with MCI

Recent discoveries indicating that the brain retains its ability to adapt and change throughout life have sparked interest in cognitive training (CT) as a possible means to postpone the development of dementia. Despite this, most research has focused on confirming the efficacy of training outcomes, with few studies examining the correlation between performance and results across various stages of training. In particular, the relationship between initial performance and the extent of improvement, the rate of learning, and the asymptotic performance level throughout the learning curve remains ambiguous. In this study, older adults underwent ten days of selective attention training using an adaptive algorithm, which enabled a detailed analysis of the learning curve's progression. Cognitive abilities were assessed before and after CT using the Mini-mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). The findings indicated that: (1) Initial performance is positively correlated with Learning amount and asymptotic performance level, and negatively correlated with learning speed; (2) Age is negatively correlated with learning speed, while it is positively correlated with the other three parameters. (3) Higher pre-training MMSE scores predicted higher post-training MMSE scores but less improvement; (4) Higher pre-training MoCA scores predicted higher post-training MoCA scores and less improvement; (5) The parameters of the learning curve did not correlate with performance on the MMSE or MoCA. These results indicate that: (1)Selective attention training using adaptive algorithms is an effective tool for cognitive intervention; (2) Older individuals with poor baseline cognitive abilities require more diversified cognitive training; (3) The study supports the compensation hypothesis.

Vision Improvement in Keratoconus Patients Trained With Perceptual Learning: A Randomized Controlled Trial

PURPOSE

To investigate the effectiveness and maintenance of perceptional learning (PL) on vision improvement in keratoconus (KC) patients corrected with spectacles.

DESIGN

Randomized, double-blind clinical trial.

METHODS

Non-progressive KC patients 9 years of age or older who had best spectacle-corrected distance visual acuity (CDVA) of 0 to 1.0 logMAR (Snellen equivalent range 20/20 to 20/200) and who were contact lenses intolerant were enrolled. Eligible subjects were randomized into PL and control groups to receive PL and placebo training for 3 months, respectively. Spectacle-corrected visual acuity, contrast sensitivity function (CSF), stereoacuity, and visual functioning and quality of life were measured at baseline, 3 months, and 6 months of follow-up. Statistics were analyzed following the intention-to-treat principle.

RESULTS

After 3 months of training, the CDVA of patients in the PL group improved as compared to the placebo group (0.17 ± 0.15 logMAR vs 0.02 ± 0.06 logMAR; P = .0006). Eight of 17 (47.06%) patients in the PL group reached CDVA improvement ≥2 lines (P = .0010). This improvement persisted for at least 6 months (from baseline) as compared to the placebo group (0.17 ± 0.17 logMAR vs 0.01 ± 0.07 logMAR; P = .0011). The increase in CSF in the PL group mainly was found for moderate spatial frequency (0.11 ± 0.17 log units at 3 cpd; 0.12 ± 0.19 log units at 6 cpd). Linear regression indicated that patients with worse initial CDVA achieved better gains in CDVA after PL (P = .009). No side effects were observed, and no subjects withdrew from the study because of training difficulties.

CONCLUSIONS

Three-month PL improved vision in KC patients, and the improvement was maintained after 3 months of treatment cessation. The results indicate that PL may be a promising therapy for KC patients with unsatisfied spectacle-corrected visual acuity.

Exogenous attention generalizes location transfer of perceptual learning in adults with amblyopia

Visual perceptual learning (VPL) is a behavioral manifestation of brain neuroplasticity. However, its practical effectiveness is limited because improvements are often specific to the trained conditions and require significant time and effort. It is critical to understand the conditions that promote learning and transfer. Covert endogenous (voluntary) and exogenous (involuntary) spatial attention help overcome VPL location specificity in neurotypical adults, but whether they also do so for people with atypical visual development is unknown. This study investigates the role of exogenous attention during VPL in adults with amblyopia, an ideal population given their asymmetrically developed, but highly plastic, visual cortex. Here we show that training on a discrimination task leads to improvements in foveal contrast sensitivity, acuity, and stereoacuity. Notably, exogenous attention helps generalize learning beyond trained spatial locations. Future large-scale studies can verify the extent to which attention enhances the effectiveness of perceptual learning during rehabilitation of visual disorders.

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Contrast sensitivity (CS)-based VPL in amblyopes improves CS, acuity and stereoacuity

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Similar improvement in trained amblyopic eye and untrained fellow eye

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Exogenous spatial attention facilitates location transfer of VPL in amblyopic adults

Testing the efficacy of vision training for presbyopia: alternating-distance training does not facilitate vision improvement compared to fixed-distance training

PURPOSE

Current evidence demonstrates the effectiveness of vision training for presbyopia. We developed and examined a training program to test the effectiveness of alternating focal distances as a training method.

METHODS

We devised a sharpness discrimination task, in which participants judged whether the stimulus was a sine- or square-wave grating, and tested in two training groups and one control group. In the alternating-distance training group (N = 8, age 49-64), participants had to alternate the fixation between a near- and far-screen. In the fixed-distance training group (N=8, age 47-65), participants fixated on the same-distance target for the whole block. Before and after the 20 training sessions, we measured the near- and far-visual acuity (VA) using the Landolt C and Early Treatment Diabetic Retinopathy Study (ETDRS) tasks and contrast sensitivity using the qCSF procedure. The control group (N=8, age 49-65) participated only in the pre- and post-tests.

RESULTS

Both training groups showed a significant improvement between the pre- and post-tests in the Landolt C task, and the improvement sizes were not significantly different between the groups. In the ETDRS task, only the fixed-distance training group showed significant improvement, although there was no significant difference between the two groups. Neither group showed improvement in the contrast sensitivity task compared to the control group.

CONCLUSION

The novel sharpness discrimination task can be an effective training method for presbyopia to prevent the deterioration of VA; however, contrary to popular belief, the effect of alternating-distance training was comparable to or even weaker than that of fixed-distance training.

The effect of initial performance on motion perception improvements is modulated by training method

Repeated practice of a perceptual task, termed "perceptual learning," can improve visual performance. Previously, the training thresholds were determined in two ways. One is that the stimulus corresponding to a certain level in individually set psychometric functions was selected as the training threshold. The other is that the certain stimulus was selected as the training threshold without consideration of individual differences. However, little is known about how the two training methods modulate perceptual learning. This study aimed to evaluate the effect of initial performance on patterns of motion perceptual learning under two methods-individually set or group averaged-for setting the training threshold. Thirty-six observers were randomly divided into individual and group thresholds. Psychometric functions, with the percentage correct as a function of coherence, were measured using the coherent motion direction identification task. For the individual threshold, each observer was trained at individualized coherence level, targeting 60% correct for each observer's psychometric function. For the group threshold, each observer was trained at one coherence level, targeting 60% correct in the group-averaged psychometric function. The threshold was reduced after training with the method of constant stimulus in both groups, indicating improvements following perceptual learning. Furthermore, observers with a poorer initial performance exhibited greater learning gains independent of the training method. Importantly, the correlation between the initial performance and learning gains was larger in the individual threshold than in the group threshold, suggesting the influence of the initial performance on the learning amount depends on the training method.

Broad and Long-Lasting Vision Improvements in Youth With Infantile Nystagmus After Home Training With a Perceptual Learning App

Current treatments for infantile nystagmus (IN), focused on dampening the oscillating eye movements, yield little to no improvement in visual functioning. It makes sense, however, to treat the visual impairments associated with IN with tailored sensory training. Recently, we developed such a training, targeting visual crowding as an important bottleneck in visual functioning with an eye-movement engaging letter discrimination task. This training improved visual performance of children with IN, but most children had not reached plateau performance after 10 supervised training sessions (3,500 trials). Here, we evaluate the effects of prolonged perceptual learning (14,000 trials) in 7-18-year-old children with IN and test the feasibility of tablet-based, at-home intervention. Results demonstrate that prolonged home-based perceptual training results in stable, long lasting visual acuity improvements at distance and near, with remarkably good transfer to reading and even stereopsis. Improvements on self-reported functional vision scores underline the clinical relevance of perceptual learning with e-health apps for individuals with IN.

Perceptual learning evidence for supramodal representation of stimulus orientation at a conceptual level

When stimulus inputs from different senses are integrated to form a coherent percept, inputs from a more precise sense are typically more dominant than those from a less precise sense. Furthermore, we hypothesized that some basic stimulus features, such as orientation, can be supramodal-represented at a conceptual level that is independent of the original modality precision. This hypothesis was tested with perceptual learning experiments. Specifically, participants practiced coarser tactile orientation discrimination, which initially had little impact on finer visual orientation discrimination (tactile vs. visual orientation thresholds = 3:1). However, if participants also practiced a functionally orthogonal visual contrast discrimination task in a double training design, their visual orientation performance was improved at both tactile-trained and untrained orientations, as much as through direct visual orientation training. The complete tactile-to-visual learning transfer is consistent with a conceptual supramodal representation of orientation unconstrained by original modality precision, likely through certain forms of input standardization. Moreover, this conceptual supramodal representation, when improved through perceptual learning in one sense, can in turn facilitate orientation discrimination in an untrained sense.

Initial performance predicts improvements in computerized cognitive training: Evidence from a selective attention task

Computerized cognitive training (CCT) has been found to improve a range of skills such as attention, working memory, inhibition control, and decision making. However, the relationship between the initial performance, amount of improvement, time constant, and asymptotic performance level in CCT is still unclear. In the current study, we performed selective attention training on college students and addressed this issue by mathematically modeling the learning curve with an exponential function. Twenty-nine students completed approximately 10 days of CCT. Presentation time served as the dependent variable and was measured by three-down/one-up adaptive algorithms. We fitted an exponential function to the estimated block thresholds during CCT and obtained three learning parameters (amount of improvement, time constant, and asymptotic performance level) for all subjects. The initial performance was defined by the sum of the amount of improvement and the asymptotic performance level. Pearson correlation analyses were conducted between the initial performance and the three leaning parameters. The initial performance was positively correlated with the amount of improvement and asymptotic performance level, but was negatively correlated with the time constant. The time constant was negatively correlated with the amount of improvement and asymptotic performance level. Poorer initial performance was linked to a larger amount of improvement, shorter time constant, and higher asymptotic threshold, which supported the compensation account. Our results may help improve the present understanding of the nature of the CCT process and demonstrate the advantages of using a customized training protocol to enhance the efficiency of cognitive training in practical applications.

Binocular summation is affected by crowding and tagging

In perceptual crowding, a letter easily recognized on its own, becomes unrecognizable if it is surrounded by other letters, an effect that confers a limit on the visual processing. Models assume that crowding is a hallmark of the periphery but that it is almost absent in the fovea. However, recently it was shown that crowding occurs in the fovea of people with an abnormal development of functional vision (amblyopia), when the stimulus is presented for a very short time. When targets and flankers are dissimilar, the crowding is reduced (tagging). Since a combination of binocular inputs increases the processing load, we investigated whether color tagging the target reduces crowding in the fovea of subjects with normal vision and determined how crowding is combined with binocular vision. The crowding effect at the fovea was significantly reduced by tagging with a color target. Interestingly, whereas binocular summation for a single letter was expected to be about 40%, it was significantly reduced and almost absent under crowding conditions. Our results are consistent with the notion that the crowding effect produces a high processing load on visual processing, which interferes with other processes such as binocular summation. We assume that the tagging effect in our experiment improved the subject's abilities (sensitivity and RT) by creating a "segmentation", i.e., a visual simulated separation between the target letter and the background. Interestingly, tagging the target with a distinct color can eliminate or reduce the crowding effect and consequently, binocular summation recovers.

Adaptation to the eye's chromatic aberration measured with an adaptive optics visual simulator

Some aspects of vision after correcting the longitudinal chromatic aberration (LCA) of the eye are not yet completely understood. For instance, correcting the LCA notably alters the through focus visual acuity (VA) curve, but it does not improve the best VA obtained for the natural case. In this work, vision with corrected LCA is further investigated by using an adaptive optics visual simulator (AOVS). VA was measured continuously during 20 minutes in 5 subjects under both natural and corrected LCA conditions to explore possible adaptation effects. Low contrast VA as a function of time exhibited a consistent and significant boost of 0.19 in decimal scale after an average time of 10.9 minutes of continuous testing. For high contrast, only one subject showed a similar increase in VA. These results suggest that some LCA neural adaptation may exist, particularly for low contrast. This adaptation impacts the performance of vision under corrected LCA, and possibly prevents measurement for immediate visual benefit. The results have practical implications for the design and visual testing of optical aids, especially those correcting, or altering, the LCA.

Visual motion perception improvements following direct current stimulation over V5 are dependent on initial performance

Transcranial direct current stimulation (tDCS) can improve visual perception. However, the effect of tDCS on visual perception is largely variable, possibly due to individual differences in initial performance. The goal of the present study was to evaluate the dependency of visual motion perception improvements on initial performance. Twenty-eight observers were randomly divided into two groups. Anodal tDCS and sham stimulation were separately applied to V5 (1.5 mA, 20 min), while observers performed a coherent motion direction identification task. The results showed that compared to sham stimulation, anodal tDCS induced a significant improvement in motion perception that lasted at least 20 min. In addition, the degree of improvement was dependent on initial performance, with a greater improvement magnitude observed for those with poorer initial performance. These results may have implications for understanding the nature of the stimulation rule and for the use of a customised stimulation protocol to enhance tDCS efficiency in practical applications.

Specificity and retention of visual perceptual learning in young children with low vision

There is evidence that a pen-and-paper training based on perceptual learning principles improves near visual acuity in young children with visual impairment. The aim of the present study is to measure specificity and retention of its training effects during one year. Sixteen visually impaired children aged 4-8 years were divided in two age- and acuity-matched groups: an early (n = 9) and late treatment group (n = 7). Training consisted of 12 sessions (2× per week for 6 weeks). Studied variables were uncrowded and crowded binocular near visual acuity (40 cm), distance visual acuity (3.0 m) and fine motor skills (Beery VMI, subtest Motor Control). In the early treatment group, we measured at 0 months (pre-training), at 2 months (post-training), at 8 months (6 months post-training) and at 14 months (12 months post-training) since inclusion. In the late treatment group, three pre-training measurements were performed at 0, 2 and 8 months, and two measurements at 0 and 6 months post-training. In the short term, training improved uncrowded and crowded near visual acuity at 0.4 m by 0.13 ± 0.03 and 0.09 ± 0.03 logMAR, respectively (mean ± SEM). Training did not affect distance acuities or Beery scores. Learning effects on uncrowded and crowded near visual acuities remained intact 6-12 months after training. We conclude that the pen-and-paper training specifically improves near visual acuities but does not transfer to distance acuities or fine motor skills. Improvements in near visual acuity are retained over time, bolstering its clinical value.

Perceptual Learning at Higher Trained Cutoff Spatial Frequencies Induces Larger Visual Improvements

It is well known that extensive practice of a perceptual task can improve visual performance, termed perceptual learning. The goal of the present study was to evaluate the dependency of visual improvements on the features of training stimuli (i.e., spatial frequency). Twenty-eight observers were divided into training and control groups. Visual acuity (VA) and contrast sensitivity function (CSF) were measured and compared before and after training. All observers in the training group were trained in a monocular grating detection task near their individual cutoff spatial frequencies. The results showed that perceptual learning induced significant visual improvement, which was dependent on the cutoff spatial frequency, with a greater improvement magnitude and transfer of perceptual learning observed for those trained with higher spatial frequencies. However, VA significantly improved following training but was not related to the cutoff spatial frequency. The results may broaden the understanding of the nature of the learning rule and the neural plasticity of different cortical areas.

The relationship between initial threshold, learning, and generalization in perceptual learning

We investigated the origin of two previously reported general rules of perceptual learning. First, the initial discrimination thresholds and the amount of learning were found to be related through a Weber-like law. Second, increased training length negatively influenced the observer's ability to generalize the obtained knowledge to a new context. Using a five-day training protocol, separate groups of observers were trained to perform discrimination around two different reference values of either contrast (73% and 30%) or orientation (25° and 0°). In line with previous research, we found a Weber-like law between initial performance and the amount of learning, regardless of whether the tested attribute was contrast or orientation. However, we also showed that this relationship directly reflected observers' perceptual scaling function relating physical intensities to perceptual magnitudes, suggesting that participants learned equally on their internal perceptual space in all conditions. In addition, we found that with the typical five-day training period, the extent of generalization was proportional to the amount of learning, seemingly contradicting the previously reported diminishing generalization with practice. This result suggests that the negative link between generalization and the length of training found in earlier studies might have been due to overfitting after longer training and not directly due to the amount of learning per se.

Vision improvement in pilots with presbyopia following perceptual learning

Israeli Air Force (IAF) pilots continue flying combat missions after the symptoms of natural near-vision deterioration, termed presbyopia, begin to be noticeable. Because modern pilots rely on the displays of the aircraft control and performance instruments, near visual acuity (VA) is essential in the cockpit. We aimed to apply a method previously shown to improve visual performance of presbyopes, and test whether presbyopic IAF pilots can overcome the limitation imposed by presbyopia. Participants were selected by the IAF aeromedical unit as having at least initial presbyopia and trained using a structured personalized perceptual learning method (GlassesOff application), based on detecting briefly presented low-contrast Gabor stimuli, under the conditions of spatial and temporal constraints, from a distance of 40 cm. Our results show that despite their initial visual advantage over age-matched peers, training resulted in robust improvements in various basic visual functions, including static and temporal VA, stereoacuity, spatial crowding, contrast sensitivity and contrast discrimination. Moreover, improvements generalized to higher-level tasks, such as sentence reading and aerial photography interpretation (specifically designed to reflect IAF pilots' expertise in analyzing noisy low-contrast input). In concert with earlier suggestions, gains in visual processing speed are plausible to account, at least partially, for the observed training-induced improvements.

Learning to see again: biological constraints on cortical plasticity and the implications for sight restoration technologies

The 'bionic eye'-so long a dream of the future-is finally becoming a reality with retinal prostheses available to patients in both the US and Europe. However, clinical experience with these implants has made it apparent that the visual information provided by these devices differs substantially from normal sight. Consequently, the ability of patients to learn to make use of this abnormal retinal input plays a critical role in whether or not some functional vision is successfully regained. The goal of the present review is to summarize the vast basic science literature on developmental and adult cortical plasticity with an emphasis on how this literature might relate to the field of prosthetic vision. We begin with describing the distortion and information loss likely to be experienced by visual prosthesis users. We then define cortical plasticity and perceptual learning, and describe what is known, and what is unknown, about visual plasticity across the hierarchy of brain regions involved in visual processing, and across different stages of life. We close by discussing what is known about brain plasticity in sight restoration patients and discuss biological mechanisms that might eventually be harnessed to improve visual learning in these patients.

Perceptual training yields rapid improvements in visually impaired youth

Visual function demands coordinated responses to information over a wide field of view, involving both central and peripheral vision. Visually impaired individuals often seem to underutilize peripheral vision, even in absence of obvious peripheral deficits. Motivated by perceptual training studies with typically sighted adults, we examined the effectiveness of perceptual training in improving peripheral perception of visually impaired youth. Here, we evaluated the effectiveness of three training regimens: (1) an action video game, (2) a psychophysical task that combined attentional tracking with a spatially and temporally unpredictable motion discrimination task, and (3) a control video game. Training with both the action video game and modified attentional tracking yielded improvements in visual performance. Training effects were generally larger in the far periphery and appear to be stable 12 months after training. These results indicate that peripheral perception might be under-utilized by visually impaired youth and that this underutilization can be improved with only ~8 hours of perceptual training. Moreover, the similarity of improvements following attentional tracking and action video-game training suggest that well-documented effects of action video-game training might be due to the sustained deployment of attention to multiple dynamic targets while concurrently requiring rapid attending and perception of unpredictable events.