1,721,005 research outputs found
Spatiotopic temporal integration of motion across saccades
No full textHumans make saccadic eye movements several times per second, on average, radically displacing the retinal image of objects from one view to the next. Why, then, is the world perceived as stable? In this study, the temporal integration of two brief motion pulses (150 ms) embedded in noise (10 s) was examined, both with maintained fixation and across eye movements. Motion coherence sensitivity was measured in a direction discrimination task as a function of the temporal delay between the two brief motion signals. When the subject made a 12 saccade from above to below the motion patch, temporal integration of motion continued across saccades, despite the fact that the retinotopic position of the stimulus changed as the result of a saccadic eye movement. This spatiotopic integration of motion occurred even when each brief motion stimulus was, by itself, below the threshold of conscious detection. Motion integration was not compulsory over the entire visual field, but depended on where the observer was looking and attending. These results suggest that the suppression of visual information during eye movements, combined with the integration of information about features of an attended object across eye movements, may be responsible for the perception of a stable world
Retinotopic temporal integration of motion across saccadic eye movements
No full textPerceptual judgments of motion require information to be integrated over time. During integration, however, the visual input may be temporarily interrupted by occlusion from other objects, or suppressed during saccadic eye movements. We examined whether motion integration continued across saccades, or whether eye movements halted or otherwise interfered with the integration of motion across separate fixations. Observers viewed a motion 'patch' (8 deg) containing two motion intervals (translation, 10 deg/sec, limited lifetime dots) embedded in a stream of random noise, and made a directional discrimination judgment. Signal-to-noise sensitivity was measured for the two separate motion signals and compared to presentations of a single motion signal. The results indicated that the signal and noise periods were integrated over a period of hundreds of milliseconds up to one second. When a saccadic eye movement (2 deg) within the boundaries of the patch was made during a period of random noise, or during a blank background, there was still integration of the motion signals (and noise) from before and after the saccade. Saccades were always orthogonal to the direction of motion. In a further test, the entire motion patch (8 × 4 deg) was displaced immediately to the new fixation position before the saccade (4.1 deg). There was no spatial overlap of the two motion patches. Nonetheless, the motion signals from the two patches were integrated when the patches were in identical retinotopic positions. These results suggest that motion signals, unlike many other forms of visual information, can be retinotopically combined across fixations. Trans-saccadic motion integration, combined with the suppression of motion perception during saccades, may play an important role in the perceived stability of the world across eye movements
Spatiotopic temporal integration of visual motion across saccadic eye movements
No full textSaccadic eye movements pose many challenges for stable and continuous vision, such as how information from successive fixations is amalgamated into a single precept. Here we show in humans that motion signals are temporally integrated across separate fixations, but only when the motion stimulus falls either on the same retinal region (retinotopic integration) or on different retinal positions that correspond to the same external spatial coordinates (spatiotopic integration). We used individual motion signals that were below detection threshold, implicating spatiotopic trans-saccadic integration in relatively early stages of visual processing such as the middle temporal area (MT) or V5 of visual cortex. The trans-saccadic buildup of important congruent visual information while irrelevant non-congruent information fades could provide a simple and robust strategy to stabilize perception during eye movements
Investigating the role of temporal processing in developmental dyslexia: Evidence for a specific deficit in rapid visual segmentation
No full textThe current study investigates the role of temporal processing in the visual domain in participants with developmental dyslexia (DD), the most common neurodevelopmental disorder, which is characterized by severe and specific difficulties in learning to read despite normal intelligence and adequate education. Specifically, our aim was to test whether DD is associated with a general impairment of temporal sensory processing or a specific deficit in temporal integration (which ensures stability of object identity and location) or segregation (which ensures sensitivity to changes in visual input). Participants with DD performed a task that measured both temporal integration and segregation using an identical sequence of two displays separated by a varying interstimulus interval (ISI) under two different task instructions. Results showed that participants with DD performed worse in the segregation task, with a shallower slope of the psychometric curve of percentage correct as a function of the ISI between the two target displays. Moreover, we found also a relationship between temporal segregation performance and text, words, and pseudowords reading speeds at the individual level. In contrast, no significant association between reading (dis)ability and temporal integration emerged. The current findings provide evidence for a difference in the fine temporal resolution of visual processing in DD and, considering the growing evidence about a link between visual temporal segregation and neural oscillations at specific frequencies, they support the idea that DD is characterized by an altered oscillatory sampling within the visual system
Shared resources between visual attention and visual working memory are allocated through rhythmic sampling
No full textAttention and visual working memory (VWM) are among the most theoretically detailed and empirically tested constructs in human cognition. Nevertheless, the nature of the interrelation between selective attention and VWM still presents a fundamental controversy: Do they rely on the same cognitive resources or not? The present study aims at disentangling this issue by capitalizing on recent evidence showing that attention is a rhythmic phenomenon, oscillating over short time windows. Using a dual-task approach, we combined a classic VWM task with a visual detection task in which we densely sampled detection performance during the time between the memory and the test array. Our results show that an increment in VWM load was related to reduced detection of near-threshold visual stimuli. Importantly, we observed an oscillatory pattern in detection at ~7.5 Hz in the low VWM load conditions, which decreased towards ~5 Hz in the high VWM load condition. These findings suggest that the frequency of this sampling rhythm changes according to the allocation of attentional resources to either the VWM or the detection task. This pattern of results is consistent with a central sampling attentional rhythm which allocates shared attentional resources both to the flow of external visual stimulation and to the internal maintenance of visual information
The effect of linguistic and visual salience in visual world studies
Full text linkResearch using the visual world paradigm has demonstrated that visual input has a rapid effect on language interpretation tasks such as reference resolution and, conversely, that linguistic material-including verbs, prepositions and adjectives-can influence fixations to potential referents. More recent research has started to explore how this effect of linguistic input on fixations is mediated by properties of the visual stimulus, in particular by visual salience. In the present study we further explored the role of salience in the visual world paradigm manipulating language-driven salience and visual salience. Specifically, we tested how linguistic salience (i.e., the greater accessibility of linguistically introduced entities) and visual salience (bottom-up attention grabbing visual aspects) interact. We recorded participants' eye-movements during a MapTask, asking them to look from landmark to landmark displayed upon a map while hearing direction-giving instructions. The landmarks were of comparable size and color, except in the Visual Salience condition, in which one landmark had been made more visually salient. In the Linguistic Salience conditions, the instructions included references to an object not on the map. Response times and fixations were recorded. Visual Salience influenced the time course of fixations at both the beginning and the end of the trial but did not show a significant effect on response times. Linguistic Salience reduced response times and increased fixations to landmarks when they were associated to a Linguistic Salient entity not present itself on the map. When the target landmark was both visually and linguistically salient, it was fixated longer, but fixations were quicker when the target item was linguistically salient only. Our results suggest that the two types of salience work in parallel and that linguistic salience affects fixations even when the entity is not visually present. © 2014 Cavicchio, Melcher and Poesio
Transsaccadic memory: Building a stable world from glance to glance
No full textDuring natural viewing, the eye samples the visual environment using a series of jerking, saccadic eye movements, separated by periods of fixation. This raises the fundamental question of how information from separate fixations is integrated into a single, coherent percept. We discuss two mechanisms that may be involved in generating our stable and continuous perception of the world. First, information about attended objects may be integrated across separate glances. To evaluate this possibility, we present and discuss data showing the transsaccadic temporal integration of motion and form. We also discuss the potential role of the re-mapping of receptive fields around the time of saccades in transsaccadic integration and in the phenomenon of saccadic mislocalization. Second, information about multiple objects in a natural scene is built up across separate glances into a coherent representation of the environment. Experiments with naturalistic stimuli show that scene memory builds up across separate glances in working memory. The combination of saccadic re-mapping, occurring on a timescale of milliseconds, and a medium-term scene memory, operating over a span of several minutes, may underlie the subjective impression of a stable visual world
Editorial: Neural Modulation of Conscious Perception: Emerging Approaches From Basic Research to Clinical Translation
Full text linkThe role of attention in central and peripheral motion integration
No full textAttention has been shown to modulate visual processing in a wide variety of tasks. We tested the influence of attention on the temporal integration of motion for both central and peripherally viewed targets (6degrees x 6degrees). Consistent with previous results, motion sensitivity for a brief motion signal (70-3500 ms) embedded in noise (10 s) increased as a function of motion duration up to a critical duration of about 1.5 s. Summation times for centrally and peripherally viewed targets were similar. An effect of eccentricity was found, however, in a double-motion task, in which two brief (150 ins) motion signals were presented with varying delays (0-7 s) of random noise between the two signals. Specifically, the maximum delay between the two signals that still supported temporal summation (summation constant) was about three times longer for centrally viewed targets (3.5-4.5 s versus 1.5-2 s). We investigated the role of spatial attention in the double-motion task by adding a concurrent color contrast discrimination task. The addition of the concurrent task dramatically reduced differences in the summation constant for central and peripheral targets, without reducing overall motion sensitivity. Thus, attention appears to specifically modulate temporal summation, suggesting that the long integration times found for motion coherence are mediated by attention. (C) 2004 Elsevier Ltd. All rights reserved
- …
