Comparison at a distance

The visual system is known to contain hard-wired mechanisms that compare the values of a given stimulus attribute at adjacent positions in the visual field; but how are comparisons performed when the stimuli are not adjacent? We ask empirically how well a human observer can compare two stimuli that are separated in the visual field. For the stimulus attributes of spatial frequency, contrast, and orientation, we have measured discrimination thresholds as a function of the spatial separation of the discriminanda. The three attributes were studied in separate experiments, but in all cases the target stimuli were briefly presented Gabor patches. The Gabor patches lay on an imaginary circle, which was centred on the fixation point and had a radius of 5 deg of visual angle. Our psychophysical procedures were designed to ensure that the subject actively compared the two stimuli on each presentation, rather than referring just one stimulus to a stored template or criterion. For the cases of spatial frequency and contrast, there was no systematic effect of spatial separation up to 10 deg. We conclude that the subject's judgment does not depend on discontinuity detectors in the early visual system but on more central codes that represent the two stimuli individually. In the case of orientation discrimination, two naive subjects performed as in the cases of spatial frequency and contrast; but two highly trained subjects showed a systematic increase of threshold with spatial separation, suggesting that they were exploiting a distal mechanism designed to detect the parallelism or non-parallelism of contours.     

The effect of exogenous spatial attention on auditory information processing

This study investigated the effect of exogenous spatial attention on auditory information processing. In Experiments 1, 2 and 3, temporal order judgment tasks were performed to examine the effect. In Experiment 1 and 2, a cue tone was presented to either the left or right ear, followed by sequential presentation of two target tones. The subjects judged the order of presentation of the target tones. The results showed that subjects heard both tones simultaneously when the target tone, which was presented on the same side as the cue tone, was presented after the target tone on the opposite side. This indicates that spatial exogenous attention was aroused by the cue tone, and facilitated subsequent auditory information processing. Experiment 3 examined whether both cue position and frequency influence the resulting information processing. The same effect of spatial attention was observed, but the effect of attention to a certain frequency was only partially observed. In Experiment 4, a tone fusion judgment task was performed to examine whether the effect of spatial attention occurred in the initial stages of hearing. The result suggests that the effect occurred in the later stages of hearing.     

Effects of spatial-frequency specific adaptation and target duration on visual persistence

Two experiments investigated the properties of visual persistence as functions of spatial frequency, stimulus duration, and pattern-specific adaptation. In Experiment 1, increasing the duration of high spatial-frequency gratings from 50 to 500 msec decreased the duration of visual persistence produced by that grating to an asymptotic level. However, low-frequency gratings produced a constant estimate of visual persistence independent of presentation time. Also, spatial-frequency specific adaptation reduced the persistence of the high-frequency gratings to this asymptotic level, but the lower frequency persistence estimates already at this level were unaffected (Experiment 2). These findings are related to possible temporal properties of the sustained and transient visual systems.     

Visible persistence of moving objects

A single line was presented in a succession of orientations, each orientation separated by a fixed angle and by a fixed interval of time, and subjects reported the number of successive lines that appeared to rotate together. The perceived number of rotating lines increased linearly with the rate of stimulus presentation, with a slope that was proportional to the spatial separation. The linear functions obtained in this first experiment predicted the results of a second experiment in which subjects adjusted the spatial and temporal variables to a discrimination threshold for seeing two rotating lines. If the slope of the linear functions is considered to be an estimate of the duration of visible persistence, then these results suggest that the visible persistence of a briefly presented stimulus increases with the distance separating that stimulus from other stimuli.     

Stimulus control of heart rate by auditory frequency and auditory pattern in pigeons

A new method was used to investigate auditory discrimination in pigeons. Basically, the method involves the repeated presentation of one stimulus preceding the single presentation of a different stimulus that is followed by shock. Stimulus control is assessed by the increase in heart rate that accompanies the presentation of the second stimulus. In Experiment 1, the efficiency of the method was explored by determining the frequency difference thresholds of pigeons at 500, 1000, 2000, and 4000 Hz. Weber fractions comparable to those reported in an earlier study using the conditioned suppression method were obtained. Experiment 2 demonstrated that, contrary to results of earlier studies, auditory temporal patterns can exercise differential stimulus control in pigeons. One stimulus consisted of the presentation (once per second) of a 1000-Hz pure tone of 150 msec duration followed by a 2000-Hz pure tone of equal duration; the other was the same except for the reversed order of the frequency components. Results indicated that the frequency pattern and not the loudness pattern of the stimuli was the cue controlling heart-rate changes.     

Tactile pattern perception by two fingers: Temporal interference and response competition

The identification of a spatial pattern (target) presented to one fingerpad may be interfered with by the presentation of a second pattern (nontarget) to either the same fingerpad or a second fingerpad. A portion of the interference appears to be due to masking and a portion to response competition. In the present study, vibrotactile spatial patterns were designed to extend over two fingerpads. Target and nontarget patterns were presented to the same two fingerpads with a temporal separation between the two patterns. The function relating target identification to the temporal separation between the target and nontarget was very similar to the functions obtained with one-finger patterns in temporal masking studies. Subsequent measurements showed that a substantial portion of the interference resulted from response competition. Pattern categorization was better when patterns were presented to two fingers on opposite hands than to two fingers on the same hand; however, there was more interference for patterns presented bilaterally than for patterns presented ipsilaterally. The results supported the conclusion that similar processes are involved in the perception of sequences of spatial patterns whether the patterns are presented to one or to two fingers.     

Spatial-frequency-dependent visible persistence and specific reading disability

Visible persistence duration for sine-wave gratings was measured in 9-year-old normal and specific-reading-disabled children. Experiment 1 investigated the influence of stimulus duration on visible persistence. The results demonstrated a Reading Group X Spatial Frequency interaction with disabled readers showing a smaller increase in persistence duration with increasing spatial frequency than controls. This interaction was greatest with stimulus durations longer than 80 msec. In Experiments 2a and 2b persistence was measured across a range of contrasts from .1 to .5. The stimulus durations employed were 100 msec in Experiment 2a and 300 msec in Experiment 2b. In both experiments, increasing contrast decreased persistence duration at 2 and 12 cycles per degree (c/deg) for the control group. In the specific-reading-disabled group, however, contrast had little effect on the persistence of 2-c/deg gratings in either experiment. In Experiment 2a the persistence of the 12-c/deg grating decreased with increasing contrast for both groups. In Experiment 2b contrast had significantly less effect on persistence duration in the specific-reading-disabled group, however, contrast had little effect on the persistence of 2-c/deg ratings in either experiment. In Experiment 2b contrast had significantly less effect on persistence duration in the specific-reading-disabled group than in the control group at 12 c/deg. Consequently, contrast had less effect on persistence in specific-reading-disabled children than in normal readers, especially at durations longer than the "critical duration" for each spatial frequency. Experiment 3 extended this finding to gratings with spatial frequencies of 4 and 8 c/deg. These results indicate a difference between normal and specific-reading-disabled children in cortical visible persistence. Two scores of visual processing were derived from the above experiments. On these scores the reading-disabled children were divided into Visual Disabled Readers (approximately 70%--eight subjects) and Nonvisual Disabled Readers (approximately 30%--four subjects). The percentages of disabled readers in each category remained constant when the sample size was increased to 61 normal and disabled readers.     

Discrimination of temporal relations by pigeons

In four experiments, pigeons were tested on a duration comparison task involving the successive presentation of two visual stimuli that varied in duration from trial to trial. Following presentation of the durations, two choice keys were lit, and reinforcement for choices was based on the temporal relation between duration of the pair. In Experiment 1, the range of durations was varied over conditions. Responding changed as an orderly function of the ratio of the two durations. There was a decrease in discrimination accuracy as average duration increased over condition but no difference in accuracy between shorter and longer problems within a duration range. There was no systematic response bias over conditions for all problems within a range, but there was a bias to report the second duration longer than the first for "long" problems within a range. In Experiment 2, the pigeons were transferred from a task involving spatially differentiated choices to one involving hue-differentiated choices. Performance was similar to that of the spatial procedure of Experiment 1. Additional analyses revealed that although information provided by a single duration of the pair was sometimes predictive of the temporal relation between pair members, responding was also based on the relation and comparison of both durations. In Experiment 3, the pigeons were exposed to a single duration range that included many durations from the four ranges of Experiment 1. Discrimination accuracy was comparable in the fourth and longest category. Manipulation of absolute reinforcement rate in Experiment 4 resulted in no chang in discrimination accuracy, suggesting that the decline in accuracy over conditions of Experiment 1 could not be attributed to decreases in reinforcement rate that accompanied lengthier durations. The results are discussed in terms of theories of animal timing, with Staddon's (1983, 1984) temporal perspective model providing the most systematic account of all aspects of performance.     

Apparent duration and spatial structure

In three experiments, we investigated the relative perceived duration of a full bandwidth iniage and a set of high- and lowpass filtered images of a scene, briefly presented on a visual display unit. In Experiment 1, the various images were compared with each other, using a paired comparison method. All images were presented for 40 msec, and observers were asked to judge which of each pair of images had the longest duration. The results showed that images containing a wide spatial frequency bandwidth were judged to be of longer duration than were images of a narrower bandwidth, regardless of whether the latter were high- or lowpass filtered. In Experiment 2, a 40-msec presentation of each of the images was compared with a presentation of a probe that was 20,40, 60, or 80 msec in duration. Observers again judged which of each pair of images had the longest duration. The results were very similar to those of Experiment 1, with wide bandwidth images being judged to be of longer duration than were narrow bandwidth images. In Experiment 3, instead of comparing the various filtered versions of the image with each other, we attempted to obtain a direct measure of perceived duration by comparing a flashing LED to a 40-msec flash of a subset of the images used in the previous experiments. The observers’ task was to adjust the duration of the LED flash to match the perceived duration of each image. The results confirmed the results of the previous experiments, again indicating that wide bandwidth images are perceived to have longer phenomenal durations than narrow bandwidth images are perceived to have. These results could be predicted from previous research in the literature on the effects of spatial frequency on perceptual lag but not from research on visual persistence. It is argued that the effects described here can probably be explained best by postulating a link between perceived duration and the integration of separately processed spatial frequency information.     

Hemispheric asymmetries for temporal information processing: transient detection versus sustained monitoring

This study investigated functional differences in the processing of visual temporal information between the left and right hemispheres (LH and RH). Participants indicated whether or not a checkerboard pattern contained a temporal gap lasting between 10 and 40 ms. When the stimulus contained a temporal signal (i.e. a gap), responses were more accurate for the right visual field-left hemisphere (RVF-LH) than for the left visual field-right hemisphere (LVF-RH). This RVF-LH advantage was larger for the shorter gap durations (Experiments 1 and 2), suggesting that the LH has finer temporal resolution than the RH, and is efficient for transient detection. In contrast, for noise trials (i.e. trial without temporal signals), there was a LVF-RH advantage. This LVF-RH advantage was observed when the entire stimulus duration was long (240 ms, Experiment 1), but was eliminated when the duration was short (120 ms, Experiment 2). In Experiment 3, where the gap was placed toward the end of the stimulus presentation, a LVF-RH advantage was found for noise trials whereas the RVF-LH advantage was eliminated for signal trials. It is likely that participants needed to monitor the stimulus for a longer period of time when the gap was absent (i.e. noise trials) or was placed toward the end of the presentation. The RH may therefore be more efficient in the sustained monitoring of visual temporal information whereas the LH is more efficient for transient detection.     

On the interplay of visuospatial and audiotemporal dominance: Evidence from a multimodal kappa effect

When participants judge multimodal audiovisual stimuli, the auditory information strongly dominates temporal judgments, whereas the visual information dominates spatial judgments. However, temporal judgments are not independent of spatial features. For example, in the kappa effect, the time interval between two marker stimuli appears longer when they originate from spatially distant sources rather than from the same source. We investigated the kappa effect for auditory markers presented with accompanying irrelevant visual stimuli. The spatial sources of the markers were varied such that they were either congruent or incongruent across modalities. In two experiments, we demonstrated that the spatial layout of the visual stimuli affected perceived auditory interval duration. This effect occurred although the visual stimuli were designated to be task-irrelevant for the duration reproduction task in Experiment 1, and even when the visual stimuli did not contain sufficient temporal information to perform a two-interval comparison task in Experiment 2. We conclude that the visual and auditory marker stimuli were integrated into a combined multisensory percept containing temporal as well as task-irrelevant spatial aspects of the stimulation. Through this multisensory integration process, visuospatial information affected even temporal judgments, which are typically dominated by the auditory modality.     

Distortions of temporal integration and perceived order caused by the interplay between stimulus contrast and duration

Stimulus contrast and duration effects on visual temporal integration and order judgment were examined in a unified paradigm. Stimulus onset asynchrony was governed by the duration of the first stimulus in Experiment 1, and by the interstimulus interval in Experiment 2. In Experiment 1, integration and order uncertainty increased when a low contrast stimulus followed a high contrast stimulus, but only when the second stimulus was 20 or 30 ms. At 10 ms duration of the second stimulus, integration and uncertainty decreased. Temporal order judgments at all durations of the second stimulus were better for a low contrast stimulus following a high contrast one. By contrast, in Experiment 2, a low contrast stimulus following a high contrast stimulus consistently produced higher integration rates, order uncertainty, and lower order accuracy. Contrast and duration thus interacted, breaking correspondence between integration and order perception. The results are interpreted in a tentative conceptual framework.     

Repetition blindness under minimum memory load: Effects of spatial and temporal proximity and the encoding effectiveness of the first item

Repetition blindness (RB) refers to the reduced performance in reporting a repeated as opposed to a nonrepeated item in rapid serial visual presentation. In Experiment 1, we found RB for two-item stimuli in uncertain locations. The magnitude of RB decreased significantly with increases in interstimulus interval, but not with increases in spatial separation, indicating that RB is determined primarily by temporal factors. In Experiment 2, we found RB when subjects were required to report only the second of two successively presented items. The magnitude of RB increased with the duration of the first item, indicating that RB is determined by the encoding effectiveness of the first item. The results of this study collectively indicate that RB is not a memory or a sensory phenomenon, but rather a perceptual phenomenon occurring at the stage of identity encoding. The findings also undermine the arguments (Kanwisher, 1987) that have been offered in favor of the type-token binding failure hypothesis and indicate instead that type-node refractoriness may be the cause of RB.     

Is there a modality effect? Evidence for visual recency and suffix effects

In Experiment 1, four groups of 16 subjects performed ordered recall of six-syllable lists in both suffix and nonsuffix conditions. Sequential presentation of the lists varied for each group. In the auditory presentation, the syllables were delivered from one location only and were read aloud by the subjects. For the visual, spatially nondistributed presentation, the syllables appeared in one location only and were read silently. For visual, spatially distributed presentations, the syllables were spread out either vertically or horizontally and were read silently. Very robust recency and suffix effects were found in the auditory presentation, as well as in visual, spatially distributed presentations. In Experiment 2, 16 subjects performed ordered recall of visually presented lists with the items spread out vertically and conflicting spatial and temporal orders. A reliable recency effect was found for the final block of trials. In Experiment 3, 16 subjects performed ordered recall in the same conditions as in Experiment 2, except that they were instructed to recall the temporal order in which the spatial positions would be filled in. A bow-shaped curve and a strong recency effect were obtained.     

Repetition effect in visual recognition of letters

This study examined the influence of the repetitive presentation of a letter on the recognition of two letters. In two experiments(4), two letters, which were either identical or not, were presented successively for a short duration at different spatial locations, and the subjects were required to identify them. In Experiment 1, the presentation time of the first letter was varied, whereas that of the second letter was constant. The results revealed that a reduced performance in identifying a second letter was observed in the case that the first letter, which was identical to the second letter, could be identified correctly. Experiment 2 examined whether or not this reduction was due to the identity of the visual shape of two letters. The first letter was presented either in the usual vertical orientation or rotated orientation by 180 degrees and the second letter was constantly presented in the usual orientation. The results revealed that a reduced performance in identifying a repeated letter was observed, regardless of the orientation of the first letter. The findings from the two experiments suggested that the identity of the information in memory was a main cause of the interference effect by repetition.     

Apparent duration and spatial structure.

In three experiments, we investigated the relative perceived duration of a full bandwidth image and a set of high- and lowpass filtered images of a scene, briefly presented on a visual display unit. In Experiment 1, the various images were compared with each other, using a paired comparison method. All images were presented for 40 msec, and observers were asked to judge which of each pair of images had the longest duration. The results showed that images containing a wide spatial frequency bandwidth were judged to be of longer duration than were images of a narrower bandwidth, regardless of whether the latter were high- or lowpass filtered. In Experiment 2, a 40-msec presentation of each of the images was compared with a presentation of a probe that was 20, 40, 60, or 80 msec in duration. Observers again judged which of each pair of images had the longest duration. The results were very similar to those of Experiment 1, with wide bandwidth images being judged to be of longer duration than were narrow bandwidth images. In Experiment 3, instead of comparing the various filtered versions of the image with each other, we attempted to obtain a direct measure of perceived duration by comparing a flashing LED to a 40-msec flash of a subset of the images used in the previous experiments. The observers' task was to adjust the duration of the LED flash to match the perceived duration of each image.(ABSTRACT TRUNCATED AT 250 WORDS)     

视觉特征捆绑：基于时间同步还是基于相同空间位置？

通过操纵客体呈现的空间位置和时间顺序,来考察视觉特征捆绑是基于相同空间位置线索还是基于时间邻近线索。在两个实验中,给被试在固定的注视点位置（固定呈现条件）或在注视点上/下位置（变换呈现条件）快速地系列呈现刺激,记录靶子前后各两个时间位置（-2、-1、+1、+2）的错觉性结合（IC）率。结果发现,在固定呈现条件下,IC更多地出现在-1和+1的时间位置上;而在变换呈现条件下,错觉性结合更多地出现在-2和+2时间位置上。为了进一步排除特定实验范式的影响,在实验3中,我们采用特征分离范式,使被分离的刺激特征同时呈现在相同（相同位置同步）或不同（不同位置同步）的空间位置上。结果表明,这两种条件下的IC率无显著差异,这说明错觉性结合不受时间同步模式的影响。综上所述,来自三个实验的结果表明,时间范围内的特征捆绑机制是按空间位置,而不是按时间邻近,线索进行的：若特征的空间位置相同,时间邻近的特征才被捆绑起来;若空间位置不同,即使时间邻近的特征也不能被捆绑到一起。     

Lateral asymmetry in the perceived sequence of speech and nonspeech stimuli

The task was to estimate the position where a click had been superimposed in a spoken sentence. Experiment 1 confirmed Fodor and Bever’s observation of an ear-asymmetry effect: the click is located earlier when it is presented to the left ear and the sentence to the right ear than with the opposite arrangement. In Experiment 2, combinations of monaural and binaural presentations were considered. They made it possible to eliminate interpretations which link the laterality effect to the fact of reaching or not reaching a particular ear and showed that the relevant factor is the relative position of the stimuli in acoustic space. Experiments 3 and 4 explored the relation between spatial separation and perceived sequence in greater detail. The relation involves a plateau: when the click comes to the left of the speech, it is preposed to a degree which depends on the amount of spatial separation; but, when it comes to the right of the speech, separation is irrelevant and the mean error is of the same order of magnitude as in a control condition without separation.     

Hemispheric differences are found in the identification,but not the detection,of low versus high spatial frequencies

The processing of sine-wave gratings presented to the left and right visual fields was examined in four experiments. Subjects were required either to detect the presence of a grating (Experiments 1 and 2) or to identify the spatial frequency of a grating (Experiments 3 and 4). Orthogonally to this, the stimuli were presented either at threshold levels of contrast (Experiments 1 and 3) or at suprathreshold levels (Experiments 2 and 4). Visual field and spatial frequency interacted when the task required identification of spatial frequency, but not when it required only stimulus detection. Regardless of contrast level (threshold, suprathreshold), high-frequency gratings were identified more readily in the right visual field (left hemisphere), whereas low-frequency gratings showed no visual field difference (Experiment 3) or were identified more readily in the left visual field (right hemisphere) (Experiment 4). Thus, hemispheric asymmetries in the processing of spatial frequencies depend on the task. These results support Sergent’s (1982) spatial frequency hypothesis, but only when the computational demands of the task exceed those required for the simple detection of the stimuli.     

Object-based perception mediates the effect of exogenous attention on temporal resolution

The effects of target distinctiveness, target placeholders, and target spatial separation on the relation between exogenous attention and temporal resolution were examined in a visual temporal order judgement (TOJ) task. When identical targets were presented at different locations within a cued or uncued placeholder, attention degraded temporal resolution (Experiment 1), but when distinct targets were presented at different locations that cueing effect disappeared (Experiment 2), and when the target placeholders were not used, attention enhanced temporal resolution for distinct targets presented at different locations (Experiment 3). Attention also degraded temporal resolution when distinct targets were presented at the same location (Experiment 4). The latter two results were then replicated in a task in which distinct targets appeared randomly at the same or different locations (Experiment 5). Clearly, the nature of the relation between exogenous attention and temporal resolution is not a straightforward one—the relative location of targets, the similarity of targets, and the presence of placeholders all qualitatively affect the cueing relation. We hypothesize a mediating role for object-related processes. Specifically, exogenous attention enhances feature binding and related object representations, which subsequently degrade temporal resolution.