Orientation Discrimination Thresholds Research Articles

Neural Substrates for Early Data Reduction in Fast Vision: A Psychophysical Investigation

To ensure survival, the visual system must rapidly extract the most important elements from a large stream of information. This necessity clashes with the computational limitations of the human brain, so a strong early data reduction is required to efficiently process information in fast vision. A theoretical early vision model, recently developed to preserve maximum information using minimal computational resources, allows efficient image data reduction by extracting simplified sketches containing only optimally informative, salient features. Here, we investigate the neural substrates of this mechanism for optimal encoding of information, possibly located in early visual structures. We adopted a flicker adaptation paradigm, which has been demonstrated to specifically impair the contrast sensitivity of the magnocellular pathway. We compared flicker-induced contrast threshold changes in three different tasks. The results indicate that, after adapting to a uniform flickering field, thresholds for image discrimination using briefly presented sketches increase. Similar threshold elevations occur for motion discrimination, a task typically targeting the magnocellular system. Instead, contrast thresholds for orientation discrimination, a task typically targeting the parvocellular system, do not change with flicker adaptation. The computation performed by this early data reduction mechanism seems thus consistent with magnocellular processing.

Rapid assessment of peripheral visual crowding.

Visual crowding, the phenomenon in which the ability to distinguish objects is hindered in cluttered environments, has critical implications for various ophthalmic and neurological disorders. Traditional methods for assessing crowding involve time-consuming and attention-demanding psychophysical tasks, making routine examination challenging. This study sought to compare trial-based Alternative Forced-Choice (AFC) paradigms using either manual or eye movement responses and a continuous serial search paradigm employing eye movement responses to evaluate their efficiency in rapidly assessing peripheral crowding. In all paradigms, we manipulated the orientation of a central Gabor patch, which could be presented alone or surrounded by six Gabor patches. We measured participants' target orientation discrimination thresholds using adaptive psychophysics to assess crowding magnitude. Depending on the paradigm, participants either made saccadic eye movements to the target location or responded manually by pressing a key or moving a mouse. We compared these paradigms in terms of crowding magnitude, assessment time, and paradigm demand. Our results indicate that employing eye movement-based paradigms for assessing peripheral visual crowding yields results faster compared to paradigms that necessitate manual responses. Furthermore, when considering similar levels of confidence in the threshold measurements, both a novel serial search paradigm and an eye movement-based 6AFC paradigm proved to be the most efficient in assessing crowding magnitude. Additionally, crowding estimates obtained through either the continuous serial search or the 6AFC paradigms were consistently higher than those obtained using the 2AFC paradigms. Lastly, participants did not report a clear difference between paradigms in terms of their perceived demand. In conclusion, both the continuous serial search and the 6AFC eye movement response paradigms enable a fast assessment of visual crowding. These approaches may potentially facilitate future routine crowding assessment. However, the usability of these paradigms in specific patient populations and specific purposes should be assessed.

The value of assessing progressive loss of red/green and yellow/blue chromatic sensitivity in glaucoma

*Correspondence: franziska.rauscher@medizin.uni-leipzig.deThe value of assessing progressive loss of red/green and yellow/blue chromatic sensitivity in glaucoma.The study employed visual stimuli designed to isolate and reveal how spatial, temporal and chromatic aspects of visual processing change from normal sensitivity to extreme loss in glaucoma. The experiments carried out examined the fovea and each of four paracentral retinal regions, arranged diagonally away from fixation at an eccentricity of 6°. Spatial vision was investigated by measuring both absolute detection thresholds and functional contrast sensitivity using Landolt ring stimuli (Ophthalmic Physiol Opt 2022;42:1363–1378). These psychophysical tests based on Landolt C optotypes measure both detection thresholds and gap orientation discrimination thresholds in the same experiments using randomly interleaved test locations. First‐order motion perception was examined by using moving stimuli embedded in static luminance contrast noise. Red/green (RG) and yellow/blue (YB) colour thresholds were measured with the Colour Assessment and Diagnosis (CAD) test, which makes use of random, dynamic luminance contrast noise (±45%) to isolate the use of RG and YB colour signals. Subjects were normal controls (n = 65) and glaucoma patients with binocular visual field defects (n = 15) classified based on their Humphrey Field Analyser mean deviation (MD) scores. The impairment of visual function varied depending on the stimulus attribute and location tested. The severity of loss increased monotonically with disease progression. For subjects with mild glaucoma (MD −0.01 to −6.00 dB), significantly more data points exceeded the upper normal threshold limits for the corresponding age for RG colour thresholds than for any other visual test (Br Med Bull 2017;122:51–77), followed by motion thresholds. This was particularly the case for the parafoveal locations when compared with the equivalent thresholds measured at the fovea. The results suggest that a multifaceted measure of binocular visual performance based on foveal and parafoveal tests of RG colour vision and first‐order motion, can best inform on the progression of glaucoma and the overall loss of visual performance for comparison with other measures of changes in the quality of life in patients with glaucoma.Keywords: Glaucoma, Visual function, Colour vision, Motion detection, Contrast, Acuity, Colour Assessment and Diagnosis, CAD.

Visual orientation discrimination skills are tightly linked with specific aspects of human intelligence.

We investigate the notion that basic visual information is acting as a building block for more complex cognitive processes in humans. Specifically, we measured individual visual orientation discrimination thresholds to report significant correlations against the total standardised intelligence quotient (IQ), verbal-IQ and non-verbal IQ scores evaluated using the Wechsler Abbreviated Scale of Intelligence Second Edition (WASI-II) test battery comprising Verbal Reasoning, Block Design, Similarities and Matrix Reasoning subtests (N = 92). A multiple linear regression analysis showed that participants' performance in our visual discrimination task, could be explained only by individual scores in Verbal Reasoning which quantifies the ability to comprehend and describe words and Matrix Reasoning, which evaluates general visual processing skills including abstract and spatial perception. Our results demonstrate that low-level visual abilities and high-level cognitive processes are more tightly interwoven together than previously thought and this result could pave the way for further research on how cognition can be defined by basic sensory processes.

Integrating electric field modeling and pre-tDCS behavioral performance to predict the individual tDCS effect on visual crowding

Objective. Transcranial direct current stimulation (tDCS) has been broadly used to modulate brain activity with both bipolar and high-definition montages. However, tDCS effects can be highly variable. In this work, we investigated whether the variability in the tDCS effects could be predicted by integrating individualized electric field modeling and individual pre-tDCS behavioral performance. Approach. Here, we first compared the effects of bipolar tDCS and 4 × 1 high-definition tDCS (HD-tDCS) with respect to the alleviation of visual crowding, which is the inability to identify targets in the presence of nearby flankers and considered to be an essential bottleneck of object recognition and visual awareness. We instructed subjects to perform an orientation discrimination task with both isolated and crowded targets in the periphery and measured their orientation discrimination thresholds before and after receiving 20 min of bipolar tDCS, 4 × 1 HD-tDCS, or sham stimulation over the visual cortex. Individual anatomically realistic head models were constructed to simulate tDCS-induced electric field distributions and quantify tDCS focality. Finally, a multiple linear regression model that used pre-tDCS behavioral performance and tDCS focality as factors was used to predict post-tDCS behavioral performance. Main results. We found that HD-tDCS, but not bipolar tDCS, could significantly alleviate visual crowding. Moreover, the variability in the tDCS effect could be reliably predicted by subjects’ pre-tDCS behavioral performance and tDCS focality. This prediction model also performed well when generalized to other two tDCS protocols with a different electrode size or a different stimulation intensity. Significance. Our study links the variability in the tDCS-induced electric field and the pre-tDCS behavioral performance in a visual crowding task to the variability in post-tDCS performance. It provides a new approach to predicting individual tDCS effects and highlights the importance of understanding the factors that determine tDCS effectiveness while developing more robust protocols.

A flexible Python-based touchscreen chamber for operant conditioning reveals improved visual perception of cardinal orientations in mice.

Natural scenes are composed of a wide range of edge angles and spatial frequencies, with a strong overrepresentation of vertical and horizontal edges. Correspondingly, many mammalian species are much better at discriminating these cardinal orientations compared to obliques. A potential reason for this increased performance could be an increased number of neurons in the visual cortex that are tuned to cardinal orientations, which is likely to be an adaptation to the natural scene statistics. Such biased angular tuning has recently been shown in the mouse primary visual cortex. However, it is still unknown if mice also show a perceptual dominance of cardinal orientations. Here, we describe the design of a novel custom-built touchscreen chamber that allows testing natural scene perception and orientation discrimination performance by applying different task designs. Using this chamber, we applied an iterative convergence towards orientation discrimination thresholds for cardinal or oblique orientations in different cohorts of mice. Surprisingly, the expert discrimination performance was similar for both groups but showed large inter-individual differences in performance and training time. To study the discrimination of cardinal and oblique stimuli in the same mice, we, therefore, applied, a different training regime where mice learned to discriminate cardinal and oblique gratings in parallel. Parallel training revealed a higher task performance for cardinal orientations in an early phase of the training. The performance for both orientations became similar after prolonged training, suggesting that learning permits equally high perceptual tuning towards oblique stimuli. In summary, our custom-built touchscreen chamber offers a flexible tool to test natural visual perception in rodents and revealed a training-induced increase in the perception of oblique gratings. The touchscreen chamber is entirely open-source, easy to build, and freely available to the scientific community to conduct visual or multimodal behavioral studies. It is also based on the FAIR principles for data management and sharing and could therefore serve as a catalyst for testing the perception of complex and natural visual stimuli across behavioral labs.

Stochastic resonance at early visual cortex during figure orientation discrimination using transcranial magnetic stimulation

Visual noise usually reduces the visibility of stimuli. However, very low contrast or subliminal visual noise can sometimes enhance the visibility of low-contrast stimuli. It has been suggested that this enhancement occurs at the visual cortex. The aims of this study are to clarify the role of the early visual cortex (V1/V2) in the enhancement effect and to clarify the relationship of the SR characteristics among different experiments. Noise was added directly to the visual cortex by using transcranial magnetic stimulation (TMS) with randomly varying intensity. The location on the scalp and the timing (stimulus onset asynchrony, SOA) of TMS were specifically adjusted to target the early visual cortex. Contrast thresholds for figure orientation discrimination were measured as a function of TMS noise intensity. With increasing TMS noise intensity the contrast threshold for figure discrimination first decreased (enhancement) and then increased (impairment). These effects were clearly dependent both on scalp location and timing (SOA). The optimum SOA was around 60 ms, while the optimum location varied across participants. Outside the optimum location and SOA values, no TMS effects were found. The enhancement effect can be accounted for by the stochastic resonance (SR) theory based on a threshold device. In addition, we reveal similarity in characteristics of the SR phenomenon between different experiments.

Emergence of crowding: The role of contrast and orientation salience.

Crowding causes difficulties in judging attributes of an object surrounded by other objects. We investigated crowding for stimuli that isolated either S-cone or luminance mechanisms or combined them. By targeting different retinogeniculate mechanisms with contrast-matched stimuli, we aim to determine the earliest site at which crowding emerges. Discrimination was measured in an orientation judgment task where Gabor targets were presented parafoveally among flankers. In the first experiment, we assessed flanked and unflanked orientation discrimination thresholds for pure S-cone and achromatic stimuli and their combinations. In the second experiment, to capture individual differences, we measured unflanked detection and orientation sensitivity, along with performance under flanker interference for stimuli containing luminance only or combined with S-cone contrast. We confirmed that orientation sensitivity was lower for unflanked S-cone stimuli. When flanked, the pattern of results for S-cone stimuli was the same as for achromatic stimuli with comparable (i.e. low) contrast levels. We also found that flanker interference exhibited a genuine signature of crowding only when orientation discrimination threshold was reliably surpassed. Crowding, therefore, emerges at a stage that operates on signals representing task-relevant featural (here, orientation) information. Because luminance and S-cone mechanisms have very different spatial tuning properties, it is most parsimonious to conclude that crowding takes place at a neural processing stage after they have been combined.

Time Course of Perceived Visual Distortion and Axial Length Growth in Myopic Children Undergoing Orthokeratology

Purpose: To establish the time course of the subjective visual function changes during the first month of orthokeratology treatment in myopic children, and to investigate how the time course variations are associated with the objective optical quality changes and the axial length growth (ALG) after 1 year of treatment.Methods: A total of 58 myopic children aged from 8 to 16 years participated in this self-controlled prospective study. All subjects were fitted with designed spherical four-zone orthokeratology lenses. Subjective visual function was evaluated with orientation discrimination threshold (ODT), and objective optical quality was quantified with the high-order aberration root-mean-square (HOA-RMS) and the changing speed of HOA. The measurements were done before the lens fitting and 1 day, 1-, 2-, and 4-weeks after lens wear. Axial length was obtained at baseline and 1-year follow-up, and ALG was defined as the difference. One-way ANOVA was conducted to compare the difference for statistical analysis.Results: After lens fitting, the ODT time courses peaked on day 1 in 28 children, 1 week in 15 children, 2 weeks in 11 children, and 4 weeks in 4 children. In contrast, the HOA-RMS steadily rose during the first month, and the changing speed of HOA was only transiently elevated on day 1 after the initial lens wear. The ALG was 0.12 ± 0.20 mm in subjects whose ODT peaked at day 1, 0.08 ± 0.09 mm in subjects whose ODT peaked on 1-week, and 0.12 ± 0.15 mm in subjects whose ODT peaked on 2-week or later. There was no difference in axial growth among the subjects whose ODT peaked at different days (P = 0.734).Conclusion: While half ODT time course resembled the changing speed of HOA with a transient elevation on day 1, about a quarter of the ODT time course resemble the steadily rising of HOA-RMS, and the rest was located in the middle. The ALGs in children with different types of ODT time courses were similar.

Grating orientation task trial numbers for short- and long-term tactile discrimination learning

Perceptual learning generally improves with training intensity, but the number of training trials sufficient for transient and long-term improvement in tactile grating orientation task (GOT) discrimination has not been systematically studied. To define reliable trial numbers for tactile discrimination learning, we compared tactile orientation discrimination performance of the right-finger following 200 and 400 training trials. Fifty-one neurologically healthy subjects were recruited. Tactile spatial acuity for orientation (parallel or orthogonal to the long axis of the finger) across different grating frequencies was assessed before, immediately after, 30 min after, and 24 h after sessions consisting of 200 training trials (50/block × 4 blocks), 400 training trials (50/block × 8 blocks), or no training (sham control). Both the 200- and 400-trial training conditions reduced the grating orientation discrimination threshold at 24 h after training. In contrast, the control condition had no effect on the grating orientation discrimination threshold. There was a negative correlation between the baseline grating orientation discrimination threshold and training-induced change in threshold (improvement) following both 200 and 400 trials. Fewer GOT trials (200) substantially prolong tactile discrimination learning, presumably by promoting the consolidation of the underlying neuroplastic mechanisms. In this widely used perceptual learning paradigm, 200 and 400 training trials appear effective for inducing short-term and long-term perceptual memory.

α-tACS over the somatosensory cortex enhances tactile spatial discrimination in healthy subjects with low alpha activity.

IntroductionSpontaneous oscillations in the somatosensory cortex, especially of the alpha (8 − 14 Hz) and gamma (60 − 80 Hz) frequencies, affect tactile perception; moreover, these oscillations can be selectively modulated by frequency‐matched transcranial alternating current stimulation (tACS) on the basis of ongoing oscillatory brain activity. To examine whether tACS can actually improve tactile perception via alpha and gamma modulation, we measured the effects of 10‐Hz and 70‐Hz tACS (α‐ and γ‐tACS) on the left somatosensory cortex on right‐finger tactile spatial orientation discrimination, and the associations between performance changes and individual alpha and gamma activities.MethodsFifteen neurologically healthy subjects were recruited into this study. Electroencephalography (EEG) was performed before the first day, to assess the normal alpha‐ and gamma‐activity levels. A grating orientation discrimination task was performed before and during 10‐Hz and 70‐Hz tACS.ResultsThe 10‐Hz tACS protocol decreased the grating orientation discrimination threshold, primarily in subjects with low alpha event‐related synchronization (ERS). In contrast, the 70‐Hz tACS had no effect on the grating orientation discrimination threshold.ConclusionsThis study showed that 10‐Hz tACS can improve tactile orientation discrimination in subjects with low alpha activity. Alpha‐frequency tACS may help identify the contributions of these oscillations to other neurophysiological and pathological processes.

Excessive visual crowding effects in developmental dyscalculia.

Visual crowding refers to the inability to identify objects when surrounded by other similar items. Crowding-like mechanisms are thought to play a key role in numerical perception by determining the sensory mechanisms through which ensembles are perceived. Enhanced visual crowding might hence prevent the normal development of a system involved in segregating and perceiving discrete numbers of items and ultimately the acquisition of more abstract numerical skills. Here, we investigated whether excessive crowding occurs in developmental dyscalculia (DD), a neurodevelopmental disorder characterized by difficulty in learning the most basic numerical and arithmetical concepts, and whether it is found independently of associated major reading and attentional difficulties. We measured spatial crowding in two groups of adult individuals with DD and control subjects. In separate experiments, participants were asked to discriminate the orientation of a Gabor patch either in isolation or under spatial crowding. Orientation discrimination thresholds were comparable across groups when stimuli were shown in isolation, yet they were much higher for the DD group with respect to the control group when the target was crowded by closely neighbouring flanking gratings. The difficulty in discriminating orientation (as reflected by the combination of accuracy and reaction times) in the DD compared to the control group persisted over several larger target flanker distances. Finally, we found that the degree of such spatial crowding correlated with impairments in mathematical abilities even when controlling for visual attention and reading skills. These results suggest that excessive crowding effects might be a characteristic of DD, independent of other associated neurodevelopmental disorders.

The Tilt Illusion and Orientation Sensitivity

Line orientation was evaluated under different observation conditions. In the first experiment, the distortion in the estimation of line orientation was 1°–9° in the presence of adjacent lines with different orientation (the tilt illusion). The illusion was stronger and the orientation discrimination thresholds were higher when the line length decreased up to 6 arcmin. For 6 arcmin lines, the illusion was approximated by a model where orientation was determined by the tilt of the minimal receptive fields (RFs) whose neurons had the maximal responses. The model was validated in the second experiment, when the minimal length for vertical and horizontal lines discrimination was determined. The minimal length was consistent with the width of the model RFs areas. The RF interactions affecting the illusion were evaluated in the third experiment where the orientation discrimination of lines with a length of 60 arcmin was studied. Age-related orientation dependencies allow a suggestion that the interactions between RFs reduce the tilt illusions.

Impairment of cyclopean surface processing by disparity-defined masking stimuli.

Binocular disparity signals allow for the estimation of three-dimensional shape, even in the absence of monocular depth cues. The perception of such disparity-defined form depends, however, on the linkage of multiple disparity measurements over space. Performance limitations in cyclopean tasks thus inform us about errors arising in disparity measurement and difficulties in the linkage of such measurements. We used a cyclopean orientation discrimination task to examine the perception of disparity-defined form. Participants were presented with random-dot sinusoidal modulations in depth and asked to report whether they were clockwise or counter-clockwise rotated. To assess the effect of different noise structures on measurement and linkage processes, task performance was measured in the presence of binocular, random-dot masks, structured as either antiphase depth sinusoids, or as random distributions of dots in depth. For a fixed number of surface dots, the ratio of mask-to-surface dots was varied to obtain thresholds for orientation discrimination. Antiphase masks were found to be more effective than random depth masks, requiring a lower mask-to-surface dot ratio to inhibit performance. For antiphase masks, performance improved with decreased cyclopean frequency, increased disparity amplitude, and/or an increase in the total number of stimulus dots. Although a cross-correlation model of disparity measurement could account for antiphase mask performance, random depth masking effects were consistent with limitations in relative disparity processing. This suggests that performance is noise-limited for antiphase masks and complexity-limited for random masks. We propose that use of differing mask types may prove effective in understanding these distinct forms of impairment.

Perceived metamorphopsia and orientation discrimination threshold before and after the surgical removal of epiretinal membrane

Perceived metamorphopsia and orientation discrimination threshold before and after the surgical removal of epiretinal membrane

The link between reading ability and visual spatial attention across development

Interacting with a cluttered and dynamic environment requires making decisions about visual information at relevant locations while ignoring irrelevant locations. Typical adults can do this with covert spatial attention: prioritizing particular visual field locations even without moving the eyes. Deficits of covert spatial attention have been implicated in developmental dyslexia, a specific reading disability. Previous studies of children with dyslexia, however, have been complicated by group differences in overall task ability that are difficult to distinguish from selective spatial attention. Here, we used a single-fixation visual search task to estimate orientation discrimination thresholds with and without an informative spatial cue in a large sample (N = 123) of people ranging in age from 5 to 70 years and with a wide range of reading abilities. We assessed the efficiency of attentional selection via the cueing effect: the difference in log thresholds with and without the spatial cue. Across our whole sample, both absolute thresholds and the cueing effect gradually improved throughout childhood and adolescence. Compared to typical readers, individuals with dyslexia had higher thresholds (worse orientation discrimination) as well as smaller cueing effects (weaker attentional selection). Those differences in dyslexia were especially pronounced prior to age 20, when basic visual function is still maturing. Thus, in line with previous theories, literacy skills are associated with the development of selective spatial attention.

Selective Colour Vision Deficits in Multiple Sclerosis at Different Temporal Stages

ABSTRACTMultiple sclerosis (MS) without optic neuritis causes color-vision deficit but the evidence for selective color deficits in parvocellular-Red/Green (PC-RG) and koniocellular-Blue/Yellow (KC-BY) pathways is inconclusive. We investigated selective color-vision deficits at different MS stages. Thirty-one MS and twenty normal participants were tested for achromatic, red-green and blue-yellow sinewave-gratings (0.5 and 2 cycles-per-degree (cpd)) contrast orientation discrimination threshold. Red-green mean threshold at 0.5cpd in established-MS and blue-yellow mean threshold in all MS participants were abnormal. These findings show blue-yellow versus red-green color test is useful in differentiating MS chronicity, which helps to better understand the mechanism of colour-vision involvement in MS.

The effect of perceptual contour orientation uncertainty on the tilt aftereffect

The tilt aftereffect (TAE) occurs when, after adapting to an oriented line, a vertical line appears to be tilted in the opposite direction. The magnitude of the TAE has been shown to relate to the salience of the adapting stimulus (e.g., its contrast) as well as to the similarity between the adapting and testing stimuli. However, the relationship between TAE and orientation uncertainty – variability in the perceived orientation of the stimulus – of either the adapting or the testing stimulus and, more importantly, change in orientation uncertainty as a function of adaptation have not previously been explored. We manipulated stimulus salience by using a variety of contour types, including real and illusory contours. Tilt aftereffects were observed even for stimuli that had much weaker or invisible illusory contours. Orientation uncertainty of the adapting stimulus, as measured by the slope of a psychometric function in orientation discrimination, was positively correlated with TAE magnitude for real and illusory contours, but not for stimuli with weak contour percepts. On an individual subject level, orientation uncertainty increased post-adaptation and was correlated with pre-adaptation uncertainty. That is, individuals with more variability in their perception of orientation before adaptation showed increased variability in orientation discrimination following adaptation. This may account for some of the variability in TAE across individuals and stimulus types and is consistent with previous findings on increased orientation discrimination thresholds post-adaptation for nearby orientations.

Interdependences between finger movement direction and haptic perception of oriented textures.

Although the natural haptic perception of textures includes active finger movements, it is unclear how closely perception and movements are linked. Here we investigated this question using oriented textures. Textures that are composed of periodically repeating grooves have a clear orientation defined by the grooves. The direction of finger movement relative to texture orientation determines the availability of temporal cues to the spatial period of the texture. These cues are absent during movements directed in line with texture orientation, whereas movements orthogonal to texture orientation maximize the temporal frequency of stimulation. This may optimize temporal cues. In Experiment 1 we tested whether texture perception gets more precise the more orthogonal the movement direction is to the texture. We systematically varied the movement direction within a 2IFC spatial period discrimination task. As expected, perception was more precise (lower discrimination thresholds) when finger movements were directed closer towards the texture orthogonal as compared to in parallel to the texture. In Experiment 2 we investigated whether people adjust movement directions to the texture orthogonal in free exploration. We recorded movement directions during free exploration of standard and comparison gratings. The standard gratings were clearly oriented. The comparison gratings did not have a clear orientation defined by grooves. Participants adjusted movement directions to the texture orthogonal only for clearly oriented textures (standards). The adjustment to texture orthogonal was present in the final movement but not in the first movement. This suggests that movement adjustment is based on sensory signals for texture orientation that were gathered over the course of exploration. In Experiment 3 we assessed whether the perception of texture orientation and movement adjustments are based on shared sensory signals. We determined perceptual thresholds for orientation discrimination and computed ‘movometric’ thresholds from the stroke-by-stroke adjustment of movement direction. Perception and movements were influenced by a common factor, the spatial period, suggesting that the same sensory signals for texture orientation contribute to both. We conclude that people optimize texture perception by adjusting their movements in directions that maximize temporal cue frequency. Adjustments are performed on the basis of sensory signals that are also used for perception.

The effect of LTP- and LTD-like visual stimulation on modulation of human orientation discrimination

Studies showing that repetitive visual stimulation protocols alter perception and induce cortical reorganization, as well-reported for the tactile domain, have been sparse. In this study, we investigated how “long-term potentiation [LTP]-like” and “long-term depression [LTD]-like” repetitive visual stimulation affects orientation discrimination ability in human observers. LTP-like stimulation with features most closely resembling the stimuli used during behavioral assessment evoked the largest improvement, while the effects were smaller in protocols that differed in shape or orientation features. This gradient suggests lower learning specificity than classical perceptual learning experiments, possibly because of an interplay of task- and feature-based factors. All modulatory effects of repetitive stimulation were superimposed on top of spontaneous task learning. Moreover, blockwise analysis revealed that LTP-like stimulation, in contrast to LTD-like or sham stimulation, prevented a loss of practice-related gain of orientation discrimination thresholds. This observation highlights a critical role of LTP-like stimulation for consolidation, typically observed during sleep.