The effect of small brightness differences on the after-effect of seen movement

Two experiments are reported. In the first experiment the after-effect of seen movement has been shown to occur with a measurable duration when there was a small difference in brightness between adjacent parts of the stimulus pattern. In the second experiment the duration of the after-effect was observed under two conditions of brightness difference; one small and the other relatively large. The difference between the durations of the aftereffect for the two conditions of brightness difference was significant. Results from these experiments have been discussed together with data from an earlier study in which the effects of brightness differences of greater magnitude were investigated. The probable function of the duration of the after-effect with respect to brightness differences over the full range of differences has been considered.     

The effect of instructions on the judgement of brightness

A brightness constancy experiment using ten subjects showed that different instructions significantly affect the subject's PSE judgement. Variations in the reflectance of the standard target and in the background and illumination of the variable target did not influence the effect of different instructions. The use of the D-ratio as constancy index in this study confirms an earlier theoretical finding that other brightness constancy ratios introduce an artefact into experimental results.     

Individual differences in pulse brightness perception

When brightness-pulse duration relations are studied with a simultaneous brightness discrimination procedure, three classes of observers emerge (Bowen & Markell, 1980). These classes are defined by whether or not observers perceive temporal brightness enhancement (the Broca-Sulzer effect) under two asynchrony conditions for pulses to be compared: simultaneous onset and simultaneous offset. Type A observers perceive brightness enhancement for both asynchrony conditions; Type B observers perceive brightness enhancement for simultaneous offset of pulses but not for simultaneous onset; Type C observers do not generate the Broca-Sulzer effect under either asynchrony condition. Here we present supplementary measures on observers of all three types: (1) magnitude estimation of the brightness of single pulses of light of varying duration, (2) modulation sensitivity for sin~wave flicker, and (3) contrast sensitivity for moving sine-wave gratings. The magnitude estimation data differentiated the three types of observers, but flicker and motion sensitivity did not. The three classes of observers probably differ in the perceptual criteria they employ in judging the brightness of isolated pulses of light; they probably do not differ in their underlying neurophysiological responses.     

Effects of hue,brightness, contrast with background,and observation time on figural dominance in ambiguous patterns

Ambiguous patterns composed of two alternate crosses of different hues and brightness on two different brightness backgrounds were viewed for 120 sec by 10 female college students. Each subject observed 92 pattern presentations (23 patterns, each pattern presented in 2 orientations and on each of 2 backgrounds). Effects of hue and brightness contrast with background were clearly demonstrated: blue was the most dominant, red the least, and green and yellow located in between. Brightness contrast of patterns with background accentuated figural dominance of the darker figures. The number of alternations increased over the observation time for hues of equal brightness; however, the relation of this measure to total duration of seeing a figure in studies of figural dominance is unclear. Theories of neural satiation, fatigue, and interaction were used in interpreting the results.     

Age differences in collaborative memory: the role of retrieval manipulations

In two experiments, we examined age differences in collaborative inhibition (reduced recall in pairs of people, relative to pooled individuals) across repeated retrieval attempts. Younger and older adults studied categorized word lists and were then given two consecutive recall tests and a recognition test. On the first recall test, the subjects were given free-report cued recall or forced-report cued recall instructions (Experiment 1) or free recall instructions (Experiment 2) and recalled the lists either alone or in collaboration with another subject of the same age group. Free-report cued recall and free recall instructions warned the subjects not to guess, whereas forcedreport cued recall instructions required them to guess. Collaborative inhibition was obtained for both younger and older adults on initial tests of free-report cued recall, forced-report cued recall, and free recall, showing that the effect generalizes across several tests for both younger and older adults. Collaborative inhibition did not persist on subsequent individual recall or recognition tests for list items. Older adults consistently falsely recalled and recognized items more than did younger adults, as had been found in previous studies. In addition, prior collaboration may exaggerate older adults’ tendency toward higher false alarms on a subsequent recognition test, but only after a free recall test. The results provide generality to the phenomenon of collaborative inhibition and can be explained by invoking concepts of strategy disruption and source monitoring.     

Sex differences and the role of figural complexity in determining the rate of mental rotation

Two experiments were conducted to investigate the effects of figural complexity on the rate of mental rotation of 3-dimensional figures and to compare the performance of men and women. Complexity was manipulated in three ways: by changing the number of blocks in the figure (7 or 10), by altering the number of turns (2 or 3), and by using outline or solid figures. In the first study, these factors were manipulated between groups of subjects. Women showed steeper slopes than men, but none of the complexity variables affected either slope or intercept for the mental rotation function. In the second study, number of turns and number of blocks were manipulated within-subjects, using only the solid figures. There were significant sex differences in both slope and intercept, and the number of blocks affected the slope of the rotation function. In both studies, a small percentage of the subjects showed nonlinear functions relating angular rotation to response time. Although the women consistently showed slower rotation functions, rate of rotation did not relate either to figural complexity or to nonlinearity. The results suggest that the rate of mental rotation is not affected by figural complexity, at least at the levels used in the present study, and that men and women employ essentially similar strategies.     

The effect of spectral manipulations on the identification of affective and linguistic prosody

We investigated the effect of various spectral manipulations on the identification of sentential prosody. Two main categories of prosody--affective (happy, angry, sad) and linguistic (statement, question, continuation)--were studied. Thirty-six subjects were presented with stimuli that were recorded by a female native speaker of American English. The stimuli were digitally manipulated to create synthesized, band-pass filtered (F0-range and F2/F3-range) and re-entrant (pitch only version of stimulus is convolved with a steady-state signal) conditions. Results of a forced-choice discrimination paradigm showed that, in general, performance is remarkably robust despite spectral manipulation, even when there is relatively little spectral information. However, performance was significantly degraded in the low band-pass and re-entrant conditions. These observations are discussed in light of the relevance of the fundamental frequency as well as syllabification for the analysis of prosodic information.     

Temporal brightness enhancement: Studies of individual differences

We have previously identified categorical individual differences in the occurrence of temporal brightness enhancement (TBE) by using a simultaneous brightness discrimination paradigm (Bowen & Markell, 1980).TBE is a nonmonotonic relation between brightness and pulse duration, pulses of intermediate duration (75–125 msec) can appear brighter than longer or shorter pulses of the same luminance. Three classes of observers can be defined based on whether they perceive TBE under one of two conditions of temporal asynchrony between a short test pulse and a longer (500 msec) comparison pulse:simultaneous onset of the pulses orsimultaneous offset. Type A observers show TBE for both asynchrony conditions; Type B observers show the effect for simultaneous offset but not simultaneous onset; Type C observers do not show TBE for either asynchrony. In the present study, we show that Type A and Type C observers maintain a constant brightness-duration relation as the asynchrony between test and comparison pulses is varied from simultaneous onset to simultaneous offset. Type B observers show a gradual shift in the brightness-duration relation as asynchrony changes. In a separate experiment, we find that practice has little effect on Type A and Type B observers but that Type C observers may change in classification to Types A and B over as few as five experimental sessions. The hypothesis that individual differences are due to differential “weighting” of chromatic (sustained) and achromatic (transient) visual channels is discussed.