The effect of an after-coming random pattern on the perception of brief visual stimuli

The perception of briefly exposed visual forms is shown to be masked by an after- coming random pattern stimulus of approximately equal intensity. This effect occurs only under certain well defined conditions; it is limited by the minimum stimulus exposure time in excess of threshold which overcomes masking (critical stimulus duration) as well as by the minimum interval between presentation of the two stimuli which permits evasion of the masking action (critical interval). Over the range of stimulus duration in which masking occurs, critical interval varied with stimulus duration in such a way that the interval multiplied by the stimulus duration equals a constant. Critical stimulus duration and critical interval at threshold are shown to vary little under a variety of conditions. The effect of the random pattern stimulus is limited to the part of the visual field to which it is presented.     

刺激呈现时间对汉字语义加工脑偏侧化的影响

以往关于汉字字词识别脑功能偏侧化的研究发现了左半球优势、右半球优势或者大脑两半球均势三种不同的结果。该研究采用一侧化Stroop范式(刺激分别只呈现于左视野、中央视野或右视野中),通过系统地改变刺激呈现时间以期探讨刺激呈现时间是可以解释这些不一致结果的可能因素之一。结果显示:对于右利手被试,在刺激呈现时间为60 ms时右半球出现了较强的Stroop效应,在刺激呈现200 ms时左右半球的Stroop效应没有表现出差异,在刺激呈现时间较长时左半球表现出较强的Stroop效应。该结果提示,随着刺激呈现时间的延长,语义优势发生了从右半球到左半球的转换。     

Learning to utilize information presented over two sensory channels

In three separate experiments, Ss were provided with auditory, visual, or simultaneous auditory and visual information in a classification task. Difficulty of classification was manipulated by varying the stimulus exposure duration. Consistent bisensory facilitation effects were noted for later trials, with interference evident on earlier trials. Exposure duration influenced rate and not amount of learning, with bisensory performance being most affected by duration. A transfer paradigm was used in Experiment III, and little if any transfer was noted between unisensory and bisensory stimulus conditions. It was concluded that Ss were extracting the most salient bisensory stimulus components from the auditory and visual modes of information into a unidimensional information configuration.     

Display polarity, stimulus exposure duration, and visual lobe shape

This study investigated the effects of visual display polarity and stimulus exposure duration on visual lobe shape. Analysis showed that regardless of display polarity and exposure duration combinations tested here, visual lobe contours were slightly irregular and asymmetric, of medium roundness, with a moderately rough boundary, and horizontally elongated with a mean length-width ratio of 1.53. Visual lobes mapped with negative display polarity were significantly rounder, slightly more regular and more symmetric along the vertical axis, compared with those mapped with positive polarity. Under the different polarity conditions, there were no significant differences in visual lobe area, perimeter, boundary smoothness, and elongation. When stimulus exposure duration increased from 200 to 400 msec. and from 200 to 300 msec., there were significant increases in the visual lobe area, perimeter, roundness, boundary smoothness, and regularity. No such changes were found when duration increased from 300 to 400 msec. Exposure durations did not have a significant effect on the shape categories of elongation and horizontal symmetry for the different stimuli. There were no statistically significant interactions between polarity and stimulus exposure duration for any of the lobe shape indexes used here.     

EFFECTS OF PERCEPTUAL QUALITY AND TASK DIFFERENCE ON THE HEMISPHERIC PROCESSING OF WORD STIMULI

Three experiments were conducted to examine the effects of stimulus exposure duration, retinal eccentricity, visual noise and task differences (physical classification and semantic classification) on the processing of Kana (Japanese phonetic symbol) words presented to the left and right visual fields. The primary findings of the three experiments were as follows. The right visual field advantage was found in the shorter exposure duration but no visual field difference was shown in the longer exposure duration condition (experiment 1). Stimulus presentation to large and small retinal eccentricity conditions revealed similar visual field difference (experiment 2). No significant visual field difference was shown in both clear and blurred stimulus presentation conditions (experiment 3). Semantic classification task revealed a right visual field advantage in all experiments whereas no visual field difference was shown in physical classification task in experiments 2 and 3. These results were discussed in terms of spatial frequency hypothesis and levels of processing hypothesis.     

Theoretical and methodological consequences of variations in exposure duration in visual laterality studies

The visual system does not instantaneously extract the entire content of a stimulus, and its resolving power is enhanced as the energy in the stimulus increases. This property of the visual system has been overlooked in previous tachistoecopic studies, the consequences of which are examined. Three groups of 12 right-handed males were presented with faces to categorize as “female” or “male,” each group at differentexposure duration, 40, 120, or 200 msec. A shift in visual field superiority was observed, from the left to the right field, as stimulus energy increased IExperiment 1). This result was replicated in Experiment 2, using a within-subject design. In Experiment 3, display energy was kept constant by reciprocally varying the duration of exposure and the level of luminance. The same shift in visual field superiority as in the previous experiments obtained when exposure duration increased. Implications of these results for future tachistoscopic studies and for a model of cerebral laterallzation are discussed. It is suggested that the right and left hemispheres may not require an equal amount of energy to efficiently engage into cognitive processing.     

Perceived duration decreases with increasing eccentricity

Previous studies examining the influence of stimulus location on temporal perception yield inhomogeneous and contradicting results. Therefore, the aim of the present study is to soundly examine the effect of stimulus eccentricity. In a series of five experiments, subjects compared the duration of foveal disks to disks presented at different retinal eccentricities on the horizontal meridian. The results show that the perceived duration of a visual stimulus declines with increasing eccentricity. The effect was replicated with various stimulus orders (Experiments 1–3), as well as with cortically magnified stimuli (Experiments 4–5), ruling out that the effect was merely caused by different cortical representation sizes. The apparent decreasing duration of stimuli with increasing eccentricity is discussed with respect to current models of time perception, the possible influence of visual attention and respective underlying physiological characteristics of the visual system.     

Iconic memory and visible persistence

There are three senses in which a visual stimulus may be said to persist psychologically for some time after its physical offset. First, neural activity in the visual system evoked by the stimulus may continue after stimulus offset (“neural persistence”). Second, the stimulus may continue to be visible for some time after its offset (“visible persistence”). Finally, information about visual properties of the stimulus may continue to be available to an observer for some time after stimulus offset (“informational persistence”). These three forms of visual persistence are widely assumed to reflect a single underlying process: a decaying visual trace that (1) consists of afteractivity in the visual system, (2) is visible, and (3) is the source of visual information in experiments on decaying visual memory. It is argued here that this assumption is incorrect. Studies of visible persistence are reviewed; seven different techniques that have been used for investigating visible persistence are identified, and it is pointed out that numerous studies using a variety of techniques have demonstrated two fundamental properties of visible persistence: theinverse duration effect (the longer a stimulus lasts, the shorter is its persistence after stimulus offset) and theinverse intensity effect (the more intense the stimulus, the briefer its persistence). Only when stimuli are so intense as to produce afterimages do these two effects fail to occur. Work on neural persistences is briefly reviewed; such persistences exist at the photoreceptor level and at various stages in the visual pathways. It is proposed that visible persistence depends upon both of these types of neural persistence; furthermore, there must be an additional neural locus, since a purely stereoscopic (and hence cortical) form of visible persistence exists. It is argued that informational persistence is defined by the use of the partial report methods introduced by Averbach and Coriell (1961) and Sperling (1960), and the term “iconic memory” is used to describe this form of persistence. Several studies of the effects of stimulus duration and stimulus intensity upon the duration of iconic memory have been carried out. Their results demonstrate that the duration of iconic memory is not inversely related to stimulus duration or stimulus intensity. It follows that informational persistence or iconic memory cannot be identified with visible persistence, since they have fundamentally different properties. One implication of this claim that one cannot investigate iconic memory by tasks that require the subject to make phenomenological judgments about the duration of a visual display. In other words, the so-called “direct methods” for studying iconic memory do not provide information about iconic memory. Another implication is that iconic memory is not intimately tied to processes going on in the visual system (as visible persistence is); provided a stimulus is adequately legible, its physical parameters have little influence upon its iconic memory. The paper concludes by pointing out that there exists an alternative to the usual view of iconic memory as a precategorical sensory buffer. According to this alternative, iconic memory is post-categorical, occurring subsequent to stimulus identification. Here, stimulus identification is considered to be a rapid automatic process which does not require buffer storage, but which provides no information about episodic properties of a visual stimulus. Information about these physical stimulus properties must, in some way, be temporarily attached to a representation of the stimulus in semantic memory; and it is this temporarily attached physical information which constitutes iconic memory.     

Postsaccadic processing of the retinal image during picture scanning

Eye movements were monitored while observers inspected photographs of natural scenes. At the end of each saccade (i.e., at the beginning of each period of steady fixation), the stimulus was replaced for a certain period of time by a uniform field (Experiment 1) or a blurred version of the stimulus scene (Experiment 2). Total fixation duration was measured as a function of the duration of the initial uniform field or the blurred image that followed the saccade. It was found that fixation duration increased proportionally with the duration of the initial replacement field, even for durations as short as 25 msec. These results suggest that the visual system uses information on the retina right after each saccade is completed and that the blurred, low-resolution information used in Experiment 2 (cutoff frequency of 0.8 cpd) is not sufficient for the requirements of picture processing in this task.     

Critical importance of exposure duration for affective discrimination of stimuli that are not recognized

Previous research has found that repeated exposure to briefly presented visual stimuli can increase the positive affect for the stimuli without enhancing their recognition. Subjects could discriminate target and distractor shapes by affective preference in the absence of recognition memory. This study examined this phenomenon as a function of stimulus exposure duration. Over exposure durations of 0, 2, 8, 12, 24, and 48 ms, the functions for affect and recognition judgments exhibited different temporal dynamics. Target selection by affect was possible at very brief exposures and was influenced little by increasing durations; target selection by recognition required longer stimulus exposures and improved with increasing durations. Affective discrimination of stimuli that are not recognized is a reliable phenomenon, but it occurs only within a narrow band of time. This parametric study has specified the relationship between exposure duration and affect and recognition judgments and has located that temporal window.     

Attention and the subjective expansion of time

During brief, dangerous events, such as car accidents and robberies, many people report that events seem to pass in slow motion, as if time had slowed down. We have measured a similar, although less dramatic, effect in response to unexpected, nonthreatening events. We attribute the subjective expansion of time to the engagement of attention and its influence on the amount of perceptual information processed. We term the effect time's subjective expansion (TSE) and examine here the objective temporal dynamics of these distortions. When a series of stimuli are shown in succession, the low-probability oddball stimulus in the series tends to last subjectively longer than the high-probability stimulus even when they last the same objective duration. In particular, (1) there is a latency of at least 120 msec between stimulus onset and the onset of TSE, which may be preceded by subjective temporal contraction; (2) there is a peak in TSE at which subjective time is particularly distorted at a latency of 225 msec after stimulus onset; and (3) the temporal dynamics of TSE are approximately the same in the visual and the auditory domains. Two control experiments (in which the methods of magnitude estimation and stimulus reproduction were used) replicated the temporal dynamics of TSE revealed by the method of constant stimuli, although the initial peak was not apparent with these methods. In addition, a third, control experiment (in which the method of single stimuli was used) showed that TSE in the visual domain can occur because of semantic novelty, rather than image novelty per se. Overall, the results support the view that attentional orienting underlies distortions in perceived duration.     

Effects of verbal labeling and exposure duration on implicit memory for visual patterns.

The present study investigated the role of verbal labeling and exposure duration in implicit memory for novel visual patterns. Encoding condition was varied in Experiment 1. Two encoding conditions discouraged verbal labeling and a third required it. In Experiment 2, exposure duration was manipulated to determine whether a new memory representation could be formed after a single 1-s exposure. The results suggest that verbal labeling is not necessary to support priming. Type of encoding did not affect implicit memory, but had a pronounced effect on explicit memory. Furthermore, a single 1-s exposure was sufficient to support priming, and priming was not further enhanced by longer stimulus exposures. In contrast, recognition performance was enhanced by a longer stimulus duration. Thus, priming effects with these novel figures are likely to be supported by newly acquired representations rather than by preexisting memory representations.     

On the time course of perceptual information that results from a brief visual presentation.

A briefly presented visual stimulus engenders an available-information function that lags behind the physical stimulus. We report two experiments that focus on the iconic-decay portion of this function, which falls to 0 over a 200-300 ms period following stimulus offset. In each experiment, to-be-reported digit strings were shown for varying durations followed by a noise mask at varying poststimulus intervals. We found the shape of the performance curve relating digit-report probability to stimulus exposure duration to be independent of stimulus-mask interstimulus interval. This finding is consistent with the proposition that the iconic-decay function's shape is independent of stimulus duration and allows us to identify this shape. We rejected exponential iconic decay for 6 of 8 observers; however, all observers' decay functions could be adequately fit by gamma decay, a generalization of exponential decay.     

Information retrieval from two rapidly consecutive stimuli: A new analysis

Data from an experiment in which Ss reported letters from two consecutive stimuli are analyzed by a nonmetric multiple regression analysis that permits the evaluation of nonlinear-e.g., quantal-hypotheses. The data are shown to contradict the hypothesis that total stimulus duration is the critical factor in response accuracy and the hypothesis of a quantal time period. Instead, they support the theory of visual persistence and continuous processing (Sperling, 1963): namely, visibility of a stimulus persists for a few lOths of a second after a stimulus has been turned off; the effect of a second stimulus exposure coming quickly after the first is to terminate visibility of the first stimulus and to substitute for it visibility of the second; information is retrieved at a rapid rate from whichever stimulus is visible.     

Increment of the extinction illusion by long stimulation

We quantitatively examined the effect of stimulus duration on the extinction illusion. A white disc was presented or not presented at an intersection of a grey grid (intersection configuration) or on a homogeneous background (background configuration). The extinction illusion was quantified as the subtraction of no-disc responses in the background configuration (ie baseline) from no-disc responses in the intersection configuration, when the disc was presented. Experiment 1 showed a temporal effect: the extinction illusion increased as stimulus duration increased; this temporal effect was observed when the disc was presented at 9 deg from the fixation point and when the stimulus duration was 1000-6000 ms. Experiment 2 showed a visual field anisotropy: the extinction illusion occurred more frequently in the upper visual field than in the lower visual field, when the stimulus duration was 200 ms; the anisotropy was not observed when the stimulus duration was 6000 ms. Experiment 3 showed an alley-length effect: when the grid alley was long, the extinction illusion occurred more frequently in the 6000 ms condition than in the 200 ms condition; the temporal effect was not observed when the grid alley was short. These results suggest that the temporal effect of the extinction illusion might be due to perceptual filling-in of luminance information of the grid alley.     

Measuring and modeling attentional dwell time

Attentional dwell time (AD) defines our inability to perceive spatially separate events when they occur in rapid succession. In the standard AD paradigm, subjects should identify two target stimuli presented briefly at different peripheral locations with a varied stimulus onset asynchrony (SOA). The AD effect is seen as a long-lasting impediment in reporting the second target, culminating at SOAs of 200?C500?ms. Here, we present the first quantitative computational model of the effect??a theory of temporal visual attention. The model is based on the neural theory of visual attention (Bundesen, Habekost, & Kyllingsb?k, Psychological Review, 112, 291?C328 2005) and introduces the novel assumption that a stimulus retained in visual short-term memory takes up visual processing-resources used to encode stimuli into memory. Resources are thus locked and cannot process subsequent stimuli until the stimulus in memory has been recoded, which explains the long-lasting AD effect. The model is used to explain results from two experiments providing detailed individual data from both a standard AD paradigm and an extension with varied exposure duration of the target stimuli. Finally, we discuss new predictions by the model.     

Stimulus spacing effects in duration perception are larger for auditory stimuli: Data and a model

Models of duration bisection have focused on the effects of stimulus spacing and stimulus modality. However, interactions between stimulus spacing and stimulus modality have not been examined systematically. Two duration bisection experiments that address this issue are reported. Experiment 1 showed that stimulus spacing influenced the classification of auditory, but not visual, stimuli. Experiment 2 used a wider stimulus range, and showed stimulus spacing effects for both visual and auditory stimuli, although the effects were larger for auditory stimuli. A version of Temporal Range Frequency Theory was applied to the data, and was used to demonstrate that the qualitative pattern of results can be captured with the single assumption that the durations of visual stimuli are less discriminable from one another than are the durations of auditory stimuli.     

Saccadic eye movements and localization of visual stimuli

Visual localization phenomena were studied before, during, and after a saccade. Light flashes of 5 and 9 msec duration presented before and during the eye movement were mislocated in the saccade direction, the localization error being a time function. When the 9-msec duration stimulus and saccade did not overlap in time, a stripe was reported, when they did not, the stimulus was perceived as a point. If a long-duration stimulus moved perpendicularly to the saccade direction with the same “sigmoidal” velocity, a curvilinear trace was perceived, regardless of the linear trace of the image on the retina. A stimulus with stabilized retinal image was perceived as a stationary point during the saccade. A possible theory to deal with the data was suggested by modifying the algebra of outflow-inflow theories.     

Apparent haptic movement

When Os were presented with ISO-Hz vibrotactile bursts at two loci on the skin of the thigh and permitted to adjust the time between burst onsets, they reported good apparent movement between the loci. The time between stimulus onsets for optimal movement was found to vary directly with the duration of the stimulus. Replication of the experiment with electrocutaneous stimuli at 1 KHz yielded similar results. Comparison of the data with results from a study of visual apparent movement revealed no difference between the two modalities for the relationship between stimulus onset intervals and stimulus duration. The significance of the results for hypotheses about the processes underlying perception of apparent movement is discussed.     

Visual persistence as measured by reaction time

Latency of reaction to onset of a visual display was subtracted from latency of reaction to offset. Persistence was defined as difference between the two latency values. Persistence was inversely related to stimulus duration and was comparable for monoptic presentation and for presentation of the first half of the stimulus duration to one eye and the second half to the other. A power function described the relation between persistence and stimulus duration. The possible effects of central intermittency on this type of reaction time measure are discussed.