Is the Contralateral Delay Activity (CDA) a robust neural correlate for Visual Working Memory (VWM) tasks? A reproducibility study

Visual working memory (VWM) allows us to actively store, update and manipulate visual information surrounding us. While the underlying neural mechanisms of VWM remain unclear, contralateral delay activity (CDA), a sustained negativity over the hemisphere contralateral to the positions of visual items to be remembered, is often used to study VWM. To investigate if the CDA is a robust neural correlate for VWM tasks, we reproduced eight CDA-related studies with a publicly accessible EEG dataset. We used the raw EEG data from these eight studies and analyzed all of them with the same basic pipeline to extract CDA. We were able to reproduce the results from all the studies and show that with a basic automated EEG pipeline we can extract a clear CDA signal. We share insights from the trends observed across the studies and raise some questions about the CDA decay and the CDA during the recall phase, which surprisingly, none of the eight studies did address. Finally, we also provide reproducibility recommendations based on our experience and challenges in reproducing these studies

Luminance texture increases perceived speed

AbstractPrevious psychophysical experiments have demonstrated that various factors can exert a considerable influence on the apparent velocity of visual stimuli. Here, we investigated the effects of superimposing static luminance texture on the apparent speed of a drifting grating. In Experiment 1, we demonstrate that superimposing static luminance texture on a drifting luminance modulated grating can produce an increase in perceived speed. This supports the hypothesis that texture changes perceived speed by providing landmarks to assess relative motion. In Experiment 2, we showed that contrary to static luminance texture, dynamic luminance texture did not increase perceived speed. This demonstrates that texture must provide reliable spatial landmarks in order to generate an increase in perceived speed. The results of Experiment 3 demonstrate that perceived speed depends on the size of the area covered by texture. This suggests that luminance texture and the motion stimulus interacted with each other over a limited spatial scale and that these local responses are then pooled to determine the speed of the motion stimulus. In Experiment 4, we showed that static texture contrast could produce a greater effect than motion stimulus contrast on perceived speed and that these effects could still be observed at brief presentation times. We discuss these findings in the context of models proposed to account for phenomena in the perception of speed

Motion processing: the most sensitive detectors differ in temporally localized and extended noise

International audienceContrast thresholds for discriminating orientation and direction of a drifting, oriented grating are usually similar to contrast detection thresholds, which suggest that the most sensitive detectors are labeled for both orientation and direction (Watson and Robson, 1981). This was found to be true in noiseless condition, but Arena et al. (2013) recently found that this was not true in localized noise (i.e., noise having the same spatiotemporal window as the target) as thresholds for discriminating direction were higher than for discriminating orientation. They suggested that this could be explained by the fact that there are more neurons selective to orientation than direction. Another possible interpretation is that, unlike contrast thresholds in absence of noise, the most sensitive detectors in localized noise were labeled for orientation, but not for direction. This hypothesis is supported by recent findings showing different processes operating in localized and extended noise (i.e., full-screen, continuously displayed noise, Allard and Cavanagh, 2011). In the current study, we evaluated contrast thresholds for orientation and direction discrimination tasks in noiseless conditions, and in noise that was either spatially localized or extended, and temporally localized or extended. We found similar orientation and direction thresholds in absence of noise and in temporally extended noise, but greater direction thresholds in temporally localized noise. This suggests that in noiseless and temporally extended noise the most sensitive detectors were labeled for both orientation and direction (e.g., direction-selective complex cells), whereas in temporally localized noise the most sensitive detectors were labeled for orientation but not direction (e.g., simple cells). We conclude that to avoid violating the noise-invariant processing assumption, external noise paradigms investigating motion processing should use noise that is temporally extended, not localized

Central and peripheral interactions in the perception of optic flow

AbstractThe purpose of this work was to evaluate the effects of central and peripheral stimulation on the perception of optic flow over large spatial extents. Coherence thresholds were measured for RDKs simulating observer translation and radial motion. Experiments 1 and 3a measured sensitivity to a range of speeds for a circular central region, for several annular regions of increasing eccentricity, and for a full-field stimulus (80° diameter). Results suggest that the spatial extent over which signals are integrated may vary in order to maximize the information available for perceptual representations. Experiments 2 and 3b evaluated central and peripheral interactions in a direction discrimination task, by comparing the effects of different signal strengths and directions in one of the two regions. The presence of noise dots (0% coherence) in either center or periphery led to a performance decrease from baseline measures. A similar decrease was observed when dots in the two regions moved in opposite directions. When dots in both regions moved in the same direction, a stronger peripheral signal led to facilitation of direction discrimination, whereas a stronger central signal did not. These findings suggest that central and peripheral inputs are not separable in the integration of optic flow, that they contribute equally to the percept under normal conditions (equal signal strength), and that peripheral stimulation seems important under ecologically relevant conditions such as poor visibility

How is complex second-order motion processed?

AbstractConverging psychophysical and electrophysiological evidence suggests that first-order (luminance-defined) complex motion types i.e., radial and rotational motion, are processed by specialized extrastriate motion mechanisms. We ask whether radial and rotational second-order (texture-defined) motion patterns are processed in a similar manner. The motion sensitivity to translating, radiating and rotating motion patterns of both first-order (luminance-modulated noise) and second-order (contrast-modulated noise) were measured for patterns presented at four different exposure durations (106, 240, 500 and 750 ms). No significant difference in motion sensitivity was found across motion type for the first-order motion class across exposure duration (i.e., from 240 to 750 ms) whereas direction-identification thresholds for radiating and rotating second-order motion were significantly greater than that of the second-order translational stimuli. Furthermore, thresholds to all second-order motion stimuli increased at a significantly faster rate with decreasing exposure duration compared to those of first-order motion. Interestingly, simple and complex second-order thresholds increased at similar rates. Taken together, the results suggest that complex second-order motion is not analyzed in a sequential manner. Rather, it seems that the same ‘hard-wired’ mechanisms responsible for complex first-order motion processing also mediate complex second-order motion, but not before the pre-processing (i.e., rectification) of local second-order motion signals

Towards the Validation of a Driving Simulator-Based Hazard Response Test for Novice Drivers

Underdeveloped hazard perception skills are associated with the higher crash risk of young novice drivers. Some driver licensing authorities use hazard perception tests (HPTs) that measure reaction times or multiple-choice responses to brief driving scenes videotaped from a vehicle traveling at legal speeds. To date, evaluations of the association between HPT scores and novice driver crash rates have been mixed. Several possible explanations for this are: high-risk novice drivers may offset good HP skills by exceeding the speed limit; current HPTs do not capture behavioral responses to hazards from candidates whose attention is engaged in the driving task; there is no established typology of driving hazards that might produce a finer-grained analysis of test results, and; current measures of HP ability may lack sensitivity. To address these potential flaws, we developed a driving simulatorbased Hazard Response Test (HRT) in which drivers respond to sixteen programmed hazard events derived from a proposed typology that combines visible or hidden, real or potential conflicts, while driving over three continuous routes. The study results indicate no statistically significant difference in crash rates between young novice and experienced drivers. However, a novel, composite measure called the Continuous Time to Collision (C-TTC) did discriminate between young novice and older experienced drivers. Additional research on the validation of this measure and further refinement of the hazard typology could contribute to the creation of a standardized, driving simulator-based HRT for use in the evaluation of novice, professional and aging drivers

Modulation of walking speed by changing optic flow in persons with stroke

<p>Abstract</p> <p>Background</p> <p>Walking speed, which is often reduced after stroke, can be influenced by the perception of optic flow (OF) speed. The present study aims to: 1) compare the modulation of walking speed in response to OF speed changes between persons with stroke and healthy controls and 2) investigate whether virtual environments (VE) manipulating OF speed can be used to promote volitional changes in walking speed post stroke.</p> <p>Methods</p> <p>Twelve persons with stroke and 12 healthy individuals walked on a self-paced treadmill while viewing a virtual corridor in a helmet-mounted display. Two experiments were carried out on the same day. In experiment 1, the speed of an expanding OF was varied sinusoidally at 0.017 Hz (sine duration = 60 s), from 0 to 2 times the subject's comfortable walking speed, for a total duration of 5 minutes. In experiment 2, subjects were exposed to expanding OFs at discrete speeds that ranged from 0.25 to 2 times their comfortable speed. Each test trial was paired with a control trial performed at comfortable speed with matching OF. For each of the test trials, subjects were instructed to walk the distance within the same time as during the immediately preceding control trial. VEs were controlled by the CAREN-2 system (Motek). Instantaneous changes in gait speed (experiment 1) and the ratio of speed changes in the test trial over the control trial (experiment 2) were contrasted between the two groups of subjects.</p> <p>Results</p> <p>When OF speed was changing continuously (experiment 1), an out-of-phase modulation was observed in the gait speed of healthy subjects, such that slower OFs induced faster walking speeds, and vice versa. Persons with stroke displayed weaker (p < 0.05, T-test) correlation coefficients between gait speed and OF speed, due to less pronounced changes and an altered phasing of gait speed modulation. When OF speed was manipulated discretely (experiment 2), a negative linear relationship was generally observed between the test-control ratio of gait speed and OF speed in healthy and stroke individuals. The slope of this relationship was similar between the stroke and healthy groups (p > 0.05, T-test).</p> <p>Conclusion</p> <p>Stroke affects the modulation of gait speed in response to changes in the perception of movement through different OF speeds. Nevertheless, the preservation of even a modest modulation enabled the persons with stroke to increase walking speed when presented with slower OFs. Manipulation of OF speed using virtual reality technology could be implemented in a gait rehabilitation intervention to promote faster walking speeds after stroke.</p

EVALUATING THE EFFECT OF A PERCEPTUAL-COGNITIVE TASK ON LANDING BIOMECHANICS OF THE LOWER LIMB

The majority of anterior cruciate ligament (ACL) injuries occur without player contact following a movement such as a landing or change of direction. Much attention has been focused on muscle strengthening to delay the biomechanical effects of muscle fatigue reduce the risk of injury. However, recent studies have indicated there may be a link between cognitive factors and non-contact ACL injuries. In this study, kinematic data was acquired from seven athletes who performed jumping and landing trials. Half of the trials performed while tracking multiple virtual objects in a 3D volume, meant to simulate a game-situation cognitive load. For all participants, significant differences were observed for several angles. Increased knee abduction, which is known to increase strain on the ACL, was observed in 4 of 7 participants