Temporal factors in visual perception as related to aging

Older Ss, in the age range 30–55 years, were compared on certain temporal characteristics of visual perception. Experiment I confirmed a previous finding that older adults required an appreciably longer exposure duration to identify forms, even when equated with younger adults on standard measures of visual acuity. Experiment 2 found that older adults have a longer critical duration over which time-intensity reciprocity holds for form identification. The results were discussed in terms of such concepts of psychological time as the psychological moment.     

Duration perception in crossmodally-defined intervals

How humans perform duration judgments with multisensory stimuli is an ongoing debate. Here, we investigated how sub-second duration judgments are achieved by asking participants to compare the duration of a continuous sound to the duration of an empty interval in which onset and offset were marked by signals of different modalities using all combinations of visual, auditory and tactile stimuli. The pattern of perceived durations across five stimulus durations (ranging from 100 ms to 900 ms) follows the Vierordt Law. Furthermore, intervals with a sound as onset (audio-visual, audio-tactile) are perceived longer than intervals with a sound as offset. No modality ordering effect is found for visualtactile intervals. To infer whether a single modality-independent or multiple modality-dependent time-keeping mechanisms exist we tested whether perceived duration follows a summative or a multiplicative distortion pattern by fitting a model to all modality combinations and durations. The results confirm that perceived duration depends on sensory latency (summative distortion). Instead, we did not find evidence for multiplicative distortions. The results of the model and the behavioural data support the concept of a single time-keeping mechanism that allows for judgments of durations marked by multisensory stimuli.     

Neural recruitment related to threat perception differs as a function of adolescent sleep

Detecting threat cues in the environment is an important aspect of social functioning. This is particularly true for adolescents as social threats become more salient and they navigate increasingly complex relationships outside of the family. Sleep relates to socioemotional processing throughout development, but the neurobiological relevance of sleep for threat perceptions in adolescence remains unknown. In the present study, 46 human adolescents (aged 14–18 years; 26 female) made judgments while undergoing a brain scan about whether unfamiliar, affectively neutral, computer‐generated faces were threatening. Prior to the scan, several indices of sleep were assessed nightly for two‐weeks using actigraphy. Sleep duration and poor sleep quality (defined as less efficiency, more awakenings, longer awakenings), factors influenced by biological and psychosocial changes during adolescence, elicited distinct neural activation patterns. Sleep duration was positively associated with activation in visual and face processing regions (occipital cortex, occipital fusiform gyrus), and this activation was linked to increased threat detection during the threat perception task. Sleep quality was negatively related to dorsolateral prefrontal cortex activation, which moderated the relation between reaction time (RT) and exposure to faces. Findings suggest reduced threat perception for adolescents with shorter sleep durations and more impulsive responding (as evinced by less consistent RT) for adolescents experiencing worse quality sleep. This study identifies an association between sleep and neural functioning relevant for socioemotional decision making during adolescence, a time when these systems undergo significant development.     

Social comparison orientation as related to two types of closeness

Two studies examined the relationship between social comparison orientation (SCO) and two types of closeness (dimensional closeness and psychological closeness) in the context of appearance-related comparisons among women. A pilot study showed that these two types were relatively independent constructs, and provided evidence for the differential validity of the constructs. Consistent with our expectations, women high in SCO perceived more dimensional closeness with other women in terms of appearance (Study 1, n = 94) and perceived more psychological closeness with other women (Study 2; n = 126) than women low in SCO. Overall, women, but especially women high in SCO, reported most dimensional closeness in response to the most attractive women and most psychological closeness in response to women of medium levels of attractiveness.     

Motion perception over long interstimulus intervals.

Recent studies using moving arrays of textured micropatterns have suggested that motion perception can be supported by two mechanisms, one quasilinear and sensitive to the motion of luminance-defined local texture, the other nonlinear and coding motion of contrast-defined envelopes of texture (Baker & Hess, 1998; Boulton & Baker, 1993b). Here we used similar patterns to study motion perception under conditions previously shown to isolate the nonlinear mechanism (low micropattern densities and positive interstimulus intervals [ISIs]. We measured direction discrimination for two-flash apparent motion over a much larger range of ISIs, and susceptibility to masking by incoherently moving "distractor" micropatterns. The results suggest that two nonlinear mechanisms can support motion perception under these conditions. One operates only for relatively short ISIs (less than c. 100 msec), is sensitive to small spatial displacements, and is relatively insensitive to distractor masking. The other operates over much longer ISIs, is insensitive to small spatial displacements, and is highly disrupted by distractor masking. These results are in line with previous studies suggesting that three mechanisms support motion perception.     

The perception of brief temporal intervals: power functions for auditory and visual stimulus intervals

Two experiments were performed to examine the role of method of estimation and the employment of a standard stimulus on the judged duration of auditory and visual stimuli presented for brief temporal intervals (0.25 to 5.0 s). The results indicate that the relationship between judged and physical duration is nearly direct and linear. Psychophysical methodology and stimulus modality exerted little influence on the obtained power functions.     

Variations in perception of short time intervals during menstrual cycle

The hypothesis that women experience heightened sensitivity and responsivity premenstrually was tested by asking 10 women to produce short time intervals at four phases of the menstrual cycle. 10 men were assigned to "pseudo-cycles" and tested as a control. The test was based on the assumption that a greater sensitivity to stimuli is reflected in a "slowing down" of subjective time. The women produced the shortest time intervals three to four days before menses, confirming the hypothesis.     

The perception of empty and filled time intervals by pigeons

Pigeons were trained in a within-subjects design to discriminate durations of a filled interval (2 s and 8 s of light) and durations of an empty interval (2 s and 8 s bound by two 500-ms light markers). Filled intervals required a response to one set of comparisons (e.g., blue vs. yellow), whereas empty intervals required a response to a different set of comparisons (e.g., red vs. green). Psychophysical testing indicated that empty intervals were judged to be longer than equivalent durations of a filled interval. This finding was replicated when the anchor durations used during training were changed to 1 s and 4 s, or 4 s and 16 s. The difference between the point of subjective equality (PSE) for the empty intervals and the PSE for filled intervals increased as the magnitude of the anchor duration pairs increased. In addition, the difference limens (DL) for empty intervals were smaller than those for filled intervals, and they also increased as the magnitude of anchor duration pairs increased. An analysis of the Weber fractions (WF; i.e., DL/PSE) provided evidence for superimposition of the empty and filled timing functions across the different sets of anchor durations. These results suggest that the accumulation of subjective time was greater for empty intervals than for filled intervals. Within the framework of scalar timing theory, this difference in timing appeared to be the result of a clock rate difference rather than a switch latency difference.     

A constant error in the perception of brief temporal intervals

Ss were presented two stimuli of equal duration separated in time. The parrs of stimuli were vibrotactile, auditory, or visual. The Ss adjusted the time between the two stimuli to be equal to the duration of the first stimulus. The results show that for stimulus durations ranging from 100 to 1,200 msec, Ss set the tune between the two stimuli too long and by a constant amount. For vibrotactfle stimuli, the constant was 596 msec; for auditory stimuli, 657 msec; and for visual stimuli, 436 msec. Changing the intensity of the vibrotactile stimuli did not change the size of the constant error. When Ss were presented two tones with a burst of white noise between the tones and adjusted the duration of the white noise to be equal to the duration of the first tone, the white noise was not adjusted too long by a constant amount. The results suggest that there is a constant error in the perception of unfilled relative to filled temporal intervals.     

Purely chromatic perception of motion in depth: two eyes as sensitive as one

Motion hyperacuity (phase) thresholds were measured for both lateral and stereoscopic oscillatory motion in both luminance and equiluminant red/green gratings of 2 cycles per degree. Thresholds for lateral chromatic motion did not exhibit the inhibitory fall-off at low temporal frequencies that was found for luminance motion. Phase thresholds for purely chromatic motion were substantially higher than those for luminance gratings, in proportion to the ratio of cone signal modulation, but they could be predicted from the corresponding contrast sensitivities for both types of stimulus. Stereomovement thresholds in luminance gratings showed the stereomovement suppression effect relative to monocular motion sensitivity previously reported for line stimuli, but purely chromatic gratings did not. Together with the lack of an inhibitory fall-off, these results imply that chromatic and luminance motion are processed by different neural pathways, and that the chrominance pathway is capable of supporting a strong percept of stereoscopic motion from purely chromatic gratings.     

Hemispheric asymmetries in the perception of musical intervals as a function of musical experience and family handedness background

This study examines the effect of musical experience and family handedness background on the categorization of musical intervals (two-note chords). Right-handed subjects, who were divided into four groups on the basis of musical training and presence (or absence) of left-handed family members, categorized musical intervals which were monaurally presented to left or right ear. The results, based on consistency and discreteness of categorization, showed: (1) Musicians' performance is superior to nonmusicians'; (2) musicians and nonmusicians differ significantly on their ear of preference; (3) family handedness background significantly affects ear of preference among musicians but not among nonmusicians.     

The two sides of perception

by Richard B. Ivry and Lynn C. Robertson, MIT Press, 1998. $55.00 (315 pages) ISBN 0 262 09034 1.