Temporal integration and contrast sensitivity in foveal and peripheral vision

Spatial contrast sensitivity functions and temporal integration functions for gratings with dark surrounds were measured at various eccentricities in photopic vision. Contrast sensitivity decreased with increasing eccentricity at all exposure durations and spatial frequencies tested. The decrease was faster at high than at low spatial frequencies, but similar at different exposure durations. When cortically similar stimulus conditions were produced at different eccentricities by M-scaling, contrast sensitivity became independent of visual field location at all exposure durations tested. The results support the view that in photopic vision spatiotemporal information processing is qualitatively similar across the visual field, and that quantitative differences result from retino-topical differences in ganglion cell sampling. For gratings of constant retinal area temporal integration (improvement of contrast sensitivity with increasing exposure duration) was more extensive at high than at low retinal spatial frequencies but independent of cortical spatial frequency and eccentricity. For M-scaled gratings temporal integration was more extensive at high than at low cortical spatial frequencies but independent of retinal spatial frequency and eccentricity. The results suggest that the primary determinant of temporal integration is not spatial frequency but grating value that is calculated as AF2 square cycles (cycle2), where A is grating area and F spatial frequency.     

Temporal factors in pattern vision

A sequence of uncorrelated randomly patterned visual stimuli (“visual noise”) is normally seen as a field of particles in “Brownian motion.” When each frame of the sequence is followed by a blank flash superimposed on the same region of the visual field, the apparent structure of the noise field is strikingly altered, its form varying with the time interval between frame and flash. At a critical interval, many dots seem to cohere, to form maggot-like objects.

Some of the factors determining this critical interval have been studied. They include the brightness, repetition frequency and exposure duration of the noise field, and the distance of its retinal image from the fovea.

The critical interval for “perceptual blanking” is quite different from that for the “maggot effect,” but the two show a suggestively similar dependence upon the duty cycle of the noise display.

It is of some neurological interest that the phenomenon is not appreciably visible with dichoptic mixing of noise and blank stimuli.     

Masking of foveal and parafoveal vision during eye fixations in reading

A window or visual mask as moved across text in synchrony with the reader's eye movements. The size of the window or mask was varied so that either information in foveal or parafoveal vision was masked on each fixation. In another experiment, the onset of the mask was delayed for a certain amount of time following the end of the saccade. The results of the experiments point out the relative importance of foveal and parafoveal vision for reading and further indicate that most of the visual information necessary for reading can be acquired during the first 50 msec that information is available during an eye fixation.     

Temporal summation in human vision: Simple reaction time measurements

Simple reaction time IRT) was measured as a function of stimulus intensity for a brief light pulse (1 msec) and a long one (300 msec). Target size, retinal position, and adapting luminance of the stimulus were varied parametrically, and the luminance value required to produce a RT of 50 msec greater than the asymptotic RT was calculated to obtain the critical duration or limit of time-intensity reciprocity. It was found that: the critical duration, even at the fovea, tends to increase with decreasing target size; the critical duration is shortest at the fovea and increases sharply with distance from the fovea; and as the adapting luminance increases, the critical duration decreases. These findings indicate that the RT technique is a sensitive measure for the stimulus conditions explored.     

Temporal factors in audition and vision: A functional emphasis

Sixty-four subjects were tested in an experiment relating temporal factors to the modality effect. The experiment involved both an immediate recall and a recognition phase. Recall scores supported a functional view of the modality effect, while the one-and two-store models only partially predicted the data. The recognition data could only be accounted for in functional terms. A non-parametric compatibility score was suggested to capture the recognition performance. The effect of a shift of input mode (in Phase I) to test mode (in Phase II) was also analyzed.     

Temporal integration in structure from motion

A temporal integration model is proposed that predicts the results reported in 4 psychophysical experiments. The main findings were (a) the initial part of a structure-from-motion (SFM) sequence influences the orientation evoked by the final part of that sequence (an effect lasting for more than 1 s), and (b) for oscillating SFM sequences, perceived slant is affected by the oscillation frequency and by the sign of the final gradient. For contracting optic flows (i.e., rotations away from the image plane), the sequence with the lowest oscillation frequency appeared more slanted; for expanding optic flows (i.e., rotations toward the image plane), the sequence with the highest oscillation frequency appeared more slanted.     

客体替代掩蔽:视觉后向掩蔽研究的新进展

传统的知觉实验通常采用视觉后向掩蔽在网膜水平上干扰对目标刺激的加工,主要有模式掩蔽和偏对比掩蔽两种形式.近年来客体替代掩蔽(简称OSM)的实验研究表明,围绕目标刺激呈现四个点也可导致目标刺激的可见性下降.OSM发生在客体表征水平上,它既是值得研究的掩蔽现象,也可以作为一种新的研究范式.本文介绍OSM的心理物理学和计算模型研究,并指出它对于认知科学的重要意义.     

Temporal integration and perception duration

Abstract.— A mathematical model is proposed for the relationship between the intensity of a stimulus as function of time and the intensity of the corresponding respcnse in the form of a conscious experience. The model is based on the assumption that the psychophysical power law is valid for the energy contained in a sliding time-window. The width and shape of this time-window will determine both the region of temporal integration and the perception duration. The consequences of this model are compared with some measurements in hearing and vision, found in the literature.     

Temporal integration of vibrotactile patterns

Three experiments were conducted to measure the temporal integration of vibrotactile patterns presented to the fingertip. In Experiment 1, letters were divided in half and the time between the onsets of the first half of the letter and second half of the letter, stimulus onset asynchrony (SOA), was varied. The recognizability of the letters declined as the SOA was increased from 9 to 100 msec. In Experiment 2, the time between two patterns constituting a masking stimulus was varied and the stimulus effectiveness in interfering with letter recognition was determined. The amount of masking increased as the SOA increased from 9 to 50 msec. In Experiment 3, the SOA between a letter and its complement (the portions of the tactile array not activated by the letter) was varied. Increasing SOA from 9 to approximately 50 msec led to increasingly accurate letter recognition. The results of the three experiments suggest that the skin is capable of complete temporal integration over a time period of less than 10 msec, and that the temporal integration function becomes asymptotic in 50 to 100 msec. The results also suggest that the onset of a vibrotactile pattern is critical for generating contours. The implications of the results for modes of generating tactile patterns and for temporal masking functions are discussed.     

Temporal integration in duration and number discrimination

Temporal integration in duration and number discrimination by rats was investigated with the use of a psychophysical choice procedure. A response on one lever ("short" response) following a 1-s white-noise signal was followed by food reinforcement, and a response on the other lever ("long" response) following a 2-s white-noise signal was also followed by food reinforcement. Either response following a signal of one of five intermediate durations was unreinforced. This led to a psychophysical function in which the probability of a long response was related to signal duration in an ogival manner. On 2 test days, a white-noise signal with 5, 6, 7, 8, or 10 segments of either 0.5-s on and 0.5-s off or 1-s on and 1-s off was presented, and a choice response following these signals was unreinforced. The probability of a long response was the same function of a segmented signal and a continuous signal if each segment was considered equivalent to 200 ms. A quantitative fit of a scalar estimation theory suggested that the latencies to initiate temporal integration and to terminate the process are both about 200 ms, and that the same internal accumulation process can be used for counting and timing.     

Semantic and pragmatic integration in vision for action

According to an influential view, the detection of action possibilities and the selection of a plan for action are two segregated steps throughout the processing of visual information. This classical approach is committed with the assumption that two independent types of processing underlie visual perception: the semantic one, which is at the service of the identification of visually presented objects, and the pragmatic one which serves the execution of actions directed to specific parts of the same objects. However, as our knowledge of vision has improved over the years, this established view has turned out to be only an approximation. This paper sets out the details of a non-modularist approach to visual perception of action possibilities and explains how to resist the lure of cognitive segregation.     

Temporal integration and vibrotactile backward masking

Subjects were presented with vibrotactile target patterns to their left index fingertips. The target patterns varied in the number of line segments that they contained and were presented in the presence or absence of a backward-masking stimulus. The stimulus onset asynchrony (SOA) between the target and masker was varied. In an identification task, subjects' errors indicated that the effect of the masker at brief SOAs was to increase the perceived number of line segments in the target. This effect diminished with increasing SOA, and at the longest SOAs subjects confused targets with patterns containing the same number of line segments but varying in how the line segments were related. In an estimation task, the effect of the masker was to increase the number of line segments estimated to be contained in the target pattern. The effect of the masker at brief SOAs is discussed in terms of an integration theory of vibrotactile backward masking. At longer SOAs, the results suggest that the masker may interfere with the extraction of relational information in the target pattern.     

Temporal coordination during bimanual reach-to-grasp movements: The role of vision

The performance of bimanual movements involving separate objects presents an obvious challenge to the visuo-motor system: Visual feedback can only be obtained from one target at a time. To overcome this challenge overt shifts in visual attention may occur so that visual feedback from both movements may be used directly (Bingham, Hughes, & Mon-Williams, 2008; Riek, Tresilian, Mon-Williams, Coppard, & Carson, 2003). Alternatively, visual feedback from both movements may be obtained in the absence of eye movements, presumably by covert shifts in attention (Diedrichsen, Nambisan, Kennerley, & Ivry, 2004). Given that the quality of information falls with increasing distance from the fixated point, can we obtain the level of information required to accurately guide each hand for precision grasping of separate objects without moving our eyes to fixate each target separately? The purpose of the current study was to examine how the temporal coordination between the upper limbs is affected by the quality of visual information available during the performance of a bimanual task. A total of 11 participants performed congruent and incongruent movements towards near and/or far objects. Movements were performed in natural, fixate-centre, fixate-left, and fixate-right vision conditions. Analyses revealed that the transport phase of incongruent movements was similar across vision conditions for the temporal aspects of both the transport and grasp, whereas the spatial aspects of grasp formation were influenced by the quality of visual feedback. We suggest that bimanual coordination of the temporal aspects of reach-to-grasp movements are not influenced solely by overt shifts in visual attention but instead are influenced by a combination of factors in a task-constrained way.     

Mechanisms of percept-percept and image-percept integration in vision: behavioral and electrophysiological evidence

Previous research has shown that the detection of a visual target can be guided not only by the temporal integration of two percepts, but also by integrating a percept and an image held in working memory. Behavioral and event-related brain potential (ERP) measures were obtained in a target detection task that required temporal integration of 2 successively presented stimuli in the left or right hemifield. Task performance was good when both displays followed each other immediately (percept-percept integration) and when displays were separated by a 300- or 900-ms interval (image-percept integration), but was poor with intermediate interstimulus intervals. An enhanced posterior negativity at electrodes contralateral to the side of the target was observed for percept-percept and for image-percept integration, demonstrating that both are based on spatiotopic representations. However, this contralateral negativity emerged later and was more sustained on trials with long interstimulus intervals, indicating that image-percept integration is slower and involves a sustained activation of working memory.     

Masking procedures can influence priming effects besides their effects on conscious perception

Masked priming has been employed to study the role of consciousness for different levels of visual processing. However, masking procedures differ systematically between studies. To examine these procedural differences we contrasted priming effects with metacontrast masking, which is often applied in the context of perceptual priming, and priming effects with sandwich pattern masking, frequently used in studies on semantic priming. Results indicate that the amount of masking neither affects perceptual nor semantic priming effects in a semantic categorization task when a metacontrast masking paradigm was used. However, perceptual and semantic priming effects increased with increasing prime visibility when a sandwich pattern masking paradigm was used. Findings suggest that different types of masking procedures affect the processing of the masked stimuli in substantially different ways even if the masking effect on conscious perception of these stimuli is comparable.