1,721,006 research outputs found
The Role of Uniform Textures in Making Texture Elements Visible in the Visual Periphery.
Full text linkThere are important differences between central and peripheral vision. With respect to shape, contours retain phenomenal sharpness, although some contours disappear if they are near other contours. This leads to some uniform textures to appear non-uniform (Honeycomb illusion, Bertamini et al., 2016). Unlike other phenomena of shape perception in the periphery, this illusion is showing how continuity of the texture does not contribute to phenomenal continuity. We systematically varied the relationship between central and peripheral regions, and we collected subjective reports (how far can one see lines) as well as judgments of line orientation. We used extended textures created with a square grid and some additional lines that are invisible when they are located at the corners of the grid, or visible when they are separated from the grid (control condition). With respects to subjective reports, we compared the region of visibility for cases in which the texture was uniform (Exp 1a), or when in a central region the lines were different (Exp 1b). There were no differences, showing no role of objective uniformity on visibility. Next, in addition to the region of visibility we measured sensitivity using a forced-choice task (line tilted left or right) (Exp 2). The drop in sensitivity with eccentricity matched the size of the region in which lines were perceived in the illusion condition, but not in the control condition. When participants were offered a choice to report of the lines were present or absent (Exp 3) they confirmed that they did not see them in the illusion condition, but saw them in the control condition. We conclude that mechanisms that control perception of contours operate differently in the periphery, and override prior expectations, including that of uniformity. Conversely, when elements are detected in the periphery, we assign to them properties based on information from central vision, but these shapes cannot be identified correctly when the task requires such discrimination
Unveiling contralesional omissions six years after stroke. Effects of top-down and bottom-up manipulations
Full text linkWe examined how spatial processing is affected by attentional load during multitasking in a chronic patient who suffered a right hemisphere stroke six years before the testing. We employed standard paper-and-pencil tests for neglect along with a new version of a well-established computerized dual-task paradigm. The latter combined a spatial processing primary task (reporting lateralized visual targets) with a concurrent secondary task (categorizing visual/auditory stimuli). Attentional load was manipulated through top-down (secondary task) and bottom-up (target size in primary task) factors. Paper-and-pencil tests did not reveal contralesional omissions. In contrast, the dual-task paradigm demonstrated greater sensitivity in detecting asymmetric spatial processing. Surprisingly, contralesional omissions occurred despite primary and secondary task stimuli did not overlap in time (i.e., secondary task stimuli were presented after the disappearance of lateralized visual targets lasting 100 ms). While both top-down and bottom-up manipulations induced contralesional omissions, their effects differed according to target size. Increased attentional load from dual-tasking impaired perception of larger contralesional targets, whereas smaller targets elicited omissions even in single-task conditions without additional multitasking effects. In this patient, very different manipulations, the first involving top-down and exclusively cognitive factors and the second involving bottom-up and purely perceptual aspects, independently modulated the level of processing resources. Both can be exploited to exacerbate very subtle (yet potentially hazardous) spatial processing deficits
Transforming a Concept in a Tool: Diagnostic and Prognostic Value of Tasks Depleting Cognitive Resources
Full text linkFast moving texture has opposite effects on the perceived speed of visible and occluded object trajectories
Full text linkIn a series of psychophysical experiments,we altered the perceived speed of a spot (target) using a grayscale texture
moving in the same (iso-motion) or opposite (anti-motion) direction of the target. In Experiment 1, using a
velocity discrimination task (2IFC), the target moved in front of the texture and was perceived faster with antimotion
than iso-motion texture. The integration and segregation of motion signals in high-level motion areas
may have accounted for the illusion. In Experiment 2, by asking observers to estimate the time-to-contact
(TTC) with a bar indicating the end of the invisible trajectory, we showed that this illusory visible speed, due
to anti- (iso-) texture, reduced (increased) the subsequent estimated duration of occluded target trajectory.
However, in Experiment 3, when the target disappeared behind the iso-motion texture, the TTC was estimated
shorter than anti- and static textures. In Experiment 4, using an interruption paradigm, we found negative
Point of Subjective Equalities (PSEs) with iso-motion but not static texture, suggesting that iso-motion led
to overestimation of the hidden speed. However, sensitivity to target speed differences, as assessed by JNDs
and d′values was not affected. Results of Experiments 3 and 4 indicate that only the iso-texture affected the estimated
target speed, but with opposite polarity compared to visible motion, suggesting a different origin of
speed bias. Because our results showthat visuospatial trackingwas facilitated by the fast iso-motion,we conclude
that motion of the occluded target was tracked by shifting visuospatial attention
Behavioural stochastic resonance across the lifespan
Full text linkStochastic resonance (SR) is the phenomenon wherein the introduction of a suitable level of noise enhances the detection of subthreshold signals in non linear systems. It manifests across various physical and biological systems, including the human brain. Psychophysical experiments have confirmed the behavioural impact of stochastic resonance on auditory, somatic, and visual perception. Aging renders the brain more susceptible to noise, possibly causing differences in the SR phenomenon between young and elderly individuals. This study investigates the impact of noise on motion detection accuracy throughout the lifespan, with 214 participants ranging in age from 18 to 82. Our objective was to determine the optimal noise level to induce an SR-like response in both young and old populations. Consistent with existing literature, our findings reveal a diminishing advantage with age, indicating that the efficacy of noise addition progressively diminishes. Additionally, as individuals age, peak performance is achieved with lower levels of noise. This study provides the first insight into how SR changes across the lifespan of healthy adults and establishes a foundation for understanding the pathological alterations in perceptual processes associated with aging
On the relationship between foveal mask interference and mental imagery in peripheral object recognition
Full text linkA delayed foveal mask affects perception of peripheral stimuli. The effect is determined by the timing of the mask and by the similarity with the peripheral stimulus. A congruent mask enhances performance, while an incongruent one impairs it. It is hypothesized that foveal masks disrupt a feedback mechanism reaching the foveal cortex. This mechanism could be part of a broader circuit associated with mental imagery, but this hypothesis has not as yet been tested. We investigated the link between mental imagery and foveal feedback. We tested the relationship between performance fluctuations caused by the foveal mask—measured in terms of discriminability (d′) and criterion (C)—and the scores from two questionnaires designed to assess mental imagery vividness (VVIQ) and another exploring object imagery, spatial imagery and verbal cognitive styles (OSIVQ). Contrary to our hypotheses, no significant correlations were found between VVIQ and the mask's impact on d′ and C. Neither the object nor spatial subscales of OSIVQ correlated with the mask's impact. In conclusion, our findings do not substantiate the existence of a link between foveal feedback and mental imagery. Further investigation is needed to determine whether mask interference might occur with more implicit measures of imagery
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