An orientation illusion analog to the rod and frame: Relational effects in the magnitude of the distortion

In previous studies, we have measured individual differences in simultaneous brightness discrimination between a long-duration (500 msec or more) comparison pulse and a set of briefer test pulses of the same luminance. Some observers judge the comparison pulse to be brighter than all test pulses in a range from 20 to 320 msec. Other observers exhibittemporal brightness enhancement: a test pulse of 80 msec for our stimulus conditions is judged brighter than the comparison pulse. Individual differences depend upon the temporal asynchrony between test and comparison pulses. Observers designated Type A show temporal brightness enhancement for both simultaneous onset of test and comparison pulse and for simultaneous offset of the pulses. Type B observers exhibit brightness enhancement for simultaneous offset of pulses but not for simultaneous onset. Type C observers do not exhibit brightness enhancement effects. Here we use both short (80 msec) and long (640 msec) pulses as the comparison stimuli. We replicate our previous pattern of individual differences for the long comparison stimulus. For the short comparison stimulus, brightness discrimination functions for the three classes of observers are exactly predicted from the patterns obtained with the conventional long comparison pulse. This confirms the generality of individual differences in pulse brightness perception and shows that they do not depend upon the particular stimulus conditions selected for the discrimination task.     

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.     

Temporal brightness enhancement studied with a large sample of observers: Evidence for individual differences in brightness perception

Brightness vs. duration relations were measured for 80 naive observers using a method in which a short pulse (10–500 msec) was compared to a pulse 500 msec longer in duration at the same luminance. Pulses were presented under two conditions of pulse asynchrony: simultaneous onset and simultaneous offset. Three classes of observers were found: Type A observers (57% of all observers) showed temporal brightness enhancement (the Broca-Sulzer effect) for both simultaneous onset and offset conditions. Type B observers (33% of the sample) showed brightness enhancement for simultaneous offset but not onset. Type C observers (10% of the sample) did not exhibit brightness enchancement under either asynchrony condition. The distribution of these classes was not affected by the specificity of instructions concerning the brightness judgment or by the sequencing (ordered vs. random) of stimuli. We analyze how these classes of observers might be explained either on the basis of differing neurophysiological mechanisms or responses or on the basis of differing psychophysical criteria. Further, we present a model of the data which illustrates how behaviorally distinct types of observers could be generated by continuous distributions within the general population of either perceptual criteria or neurophysiological responses.     

Temporal summation and reaction time to double-light pulses at suprathreshold levels

Temporal summation of the visual system was studied at suprathreshold levels by measuring reaction time (RT) to the double pulses that were equal in luminance (L) and duration. The RTs were determined as functions of L and the stimulus onset asynchrony (SOA) between the onsets of the two pulses. The relation between RT and L obtained for a given SOA was found to be a power function with the exponent 1/3. The function relating L to SOA was then derived for each of three criterion RTs. The L-SOA relationship indicated partial summation at SOAs shorter than about 20 msec. Inhibition was observed at SOAs longer than about 80 msec. These findings were consistent with the predictions from a temporal integration model.     

Anatomy of a flash. 1. Two-peak masking and a temporal filling-in

A modified paradigm of Crawford masking was used to link masking to brightness fluctuation, as distinct from flash brightness. Thresholds were measured for a 10 ms incremental pulse (the 'probe') presented before, during, or after a 500 ms pulse (the 'flash'). Both pulses were spatially coextensive with the background field, thus the criterion for probe detection was purely temporal. The flash occurred either in the tested eye, the opposite eye, or in both eyes. In all conditions, masking was strongly bimodal: thresholds peaked near flash onset and flash offset. The flash was perceived as a unitary event. Bimodal masking is attributed to cortical on-and off-effects, as (i) dichoptic masking was strong and (ii) the same incremental probe was masked by either incremental or decremental flashes. Strikingly, monocular probe thresholds were about equally elevated by binocular as by monocular flashes, although the binocular flashes were brighter. Therefore, some monocular features can be preserved in the larger net binocular response. A general conclusion is that masking depends on the same transient neural responses that bring about a brightness fluctuation, whereas the appearance of the flash as a single event, a unitary change of brightness, depends on a different mechanism, perhaps a sustained response that performs a temporal filling-in.     

The induced asynchrony effect: Its role in visual judgments of temporal order and its relation to other dynamic perceptual phenomena

A context-induced “illusion” in visual judgments of temporal order, termed the induced asynchrony effect (IAE), is reported. It consists of an apparent ordering in time of two simultaneous light onsets, produced by the preceding, asynchronous offsets of two other lights. The joint effect of a real stimulus onset asynchrony and a preceding stimulus offset asynchrony bn judgments of onset order appears to be additive, given a Gaussian transformation of response probability. This result is shown to be consistent with a simple statistical decision model, which provides a conceptual framework for drawing inferences from temporal order judgment data. However, it is emphasized that certain interpretations of such models are not empirically testable on the basis of temporal order data alone. An attempt is made to relate the IAE to three other dynamic perceptual phenomena; all four effects may reflect a tendency of observers to perceive the velocity of apparent motion as being constant. Questions raised by the demonstration of the IAE are discussed, and directions for further research are suggested.     

Sex role correlates of stress-prone type a behavior in college students

This study considered the direct and interactive relationships between three sex role variables and Type A/Type B behavior in college students of both sexes. As predicted, Type A college women were more masculine than Type B controls; Type A females were not less feminine, however, as had been expected. No relationship was found between masculine or feminine sex role behavior and Type A status in college men, consistent with the results of an earlier study. Both male and female Type As revealed weaker gender schemas than Type B controls. Analysis of the conjoint variation of all three sex role components revealed no relationships for either Type A or Type B men. Type A women presented an unusual asynchrony between these components in light of the expected positive relation between stereotyped sex role identity (femininity) and sensitivity to stereotyped differences between women and men (strong gender-schematic processing). Nontraditional female Type As, who were more masculine than feminine, demonstrated strong gender schemas. Traditional female Type As, more feminine than masculine, displayed weak gender schemas. Type B women did not display these unusual sex role linkages.     

Bloch’s law and a Poisson counting model for simple reaction time to light

A series of three experiments was conducted with identical design as an earlier series (Hildreth, 1973). Its purpose was (1) to determine whether Bloch’s law holds for simple reaction time (RT) to still lower intensity visual stimuli, and (2) to provide data for testing a stochastic generalization of the temporal integration model (TI-ED) reported earlier. RT means were found to agree with Bloch’s law for durations below 48 msec. By a statistical test, Bloch’s law was shown to hold for both means and standard deviations below about 65 msec. Latency statistics—means and standard deviations—were predicted by a Poisson process counting model. This model assumes that a number of identical, parallel Poisson processes, activated by light, with pulse interarrival times decreasing with light intensity, trigger light detection when a critical number of pulses arrive at a counting center. For the intensities investigated, both the estimated number of Poisson processes and critical number of pulses required for detection range between 8 and 13. The model predicts the Broca-Sulzer effect for mean RTs which is observed in several of these experiments.     

Studies in auditory timing: 1. Simple patterns

Listeners' accuracy in discriminating one temporal pattern from another was measured in three psychophysical experiments. When the standard pattern consisted of equally timed (isochronic) brief tones, whose interonset intervals (IOIs) were 50, 100, or 200 msec, the accuracy in detecting an asynchrony or deviation of one tone in the sequence was about as would be predicted from older research on the discrimination of single time intervals (6%-8% at an IOI of 200 msec, 11%-12% at an IOI of 100 msec, and almost 20% at an IOI of 50 msec). In a series of 6 or 10 tones, this accuracy was independent of position of delay for IOIs of 100 and 200 msec. At 50 msec, however, accuracy depended on position, being worst in initial positions and best in final positions. When one tone in a series of six has a frequency different from the others, there is some evidence (at IOI = 200 msec) that interval discrimination is relatively poorer for the tone with the different frequency. Similarly, even if all tones have the same frequency but one interval in the series is made twice as long as the others, temporal discrimination is poorer for the tones bordering the longer interval, although this result is dependent on tempo or IOI. Results with these temporally more complex patterns may be interpreted in part by applying the relative Weber ratio to the intervals before and after the delayed tone. Alternatively, these experiments may show the influence of accent on the temporal discrimination of individual tones.     

Left hemisphere selectivity for processing duration in normal subjects

The role of the left cerebral hemisphere for the discrimination of duration was examined in a group of normal subjects. Two tasks were presented: the first required a reaction-time response to the offset of monaural pulse sequences varying in interpulse duration, and the second required the discrimination of small differences in durations, within a delayed-comparison paradigm. In each task a right-ear advantage was obtained when the durations were 50 msec or less. No ear advantage was obtained for the larger durations of 67 to 120 msec. Since the perceptual distinctiveness of phonemes may be provided by durations approximating 50 msec, the nature of the relationship between the left hemisphere's role in temporal processing and speech processing may be elaborated.     

Electrocutaneous stimulation L The effects of stimulus parameters on absolute threshold

Thresholds for detecting electrical stimulation were measured as a function of (1) body locus, (2) electrode configuration, (3) stimulus waveform, and (4) pulse duration. The results were: (1) the forehead gave slightly, but not reliably, lower thresholds than the abdomen; (2) concentric electrodes gave slightly, but not reliably, lower thresholds than unifocal electrodes; (3) cathodal monophasic (?) pulses and biphasic pulses (+/? and ?/+) gave identical thresholds, while anodal monophasic (+) pulses gave higher thresholds; and (4) thresholds decreased as pulse duration increased up to .5 msec, but changed less with longer pulses.     

Discrimination of visually perceived intervals of time

The discrimination of short intervals of time, demarcated by a foveally presented spatially distinct double pulse of light, was studied under several conditions of pulse intensity, angular diameter, and duration. We defined temporal acuity as a measure of discrimination capacity in terms of d′ values. It is shown that the acuity mechanism uses largely integrated information—in the spatial and temporal domain, up to at least 56′ and 32 msec, respectively. Acuity increases slightly with increasing integrated pulse energy, but seems quite independent of the presence of an adapting field of appreciable brightness. Studies on the effect of the foveal site aimed at by the pulses of light have shown that temporal projections lead to significantly poorer acuity values than nasal projections. Monoptic and dichoptic stimulation, however, are fully equivalent.     

Laterality differences and shifts as a function of tactile temporal pattern complexity: Implications for differential processing strategies of the cerebral hemispheres

Summary The ability of subjects with a right-hand or left-hand preference to report accurately the number of tactile pulses in temporal sequences presented to preferred and nonpreferred hands was investigated as a function of temporal pattern complexity which varied in terms of intrinsic temporal relations among successive pulses and ranged from slow regular (periodic) sequences of small numbers of pulses to fast irregular (aperiodic) sequences of large numbers of pulses. As the complexity of the pattern increased in terms of pulse number, presentation rate, pulse density, and pulse aperiodicity, all subjects, for both preferred- and nonpreferred-hand stimulation, were increasingly less accurate in reporting the number of pulses in a temporal pattern. Most interesting was the finding that although hand-preference groups did not differ reliably in overall report accuracy, both groups showed a consistent shift in report accuracy from preferred- to nonpreferred-hand stimulation when patterns had more than seven pulses; furthermore, these shifts occurred for all presentation rates and pulse periodicities. A possible relationship between hand preference and cerebral psychological organization is suggested and the data are discussed in terms of the laterality differences reflecting basic underlying cerebral asymmetries in stimulus processing.These investigations were supported by Grant A8621 from the National Research Council of Canada. This paper was prepared while the author was a Visiting Researcher at the Department of Psychology, University of Stockholm, and supported, in part, by a Leave Fellowship awarded by the Social Sciences and Humanities Research Council of Canada. I would like to thank Gordon Tanne for his assistance in data collection and analysis. Requests for offprints should be sent to E.C. Lechelt, Department of Psychology, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.     

Type A behavior pattern and the judgment of control

We investigated the control judgments of Type A and B actors and observers after five tasks in which actual response-outcome contingency and success were varied systematically. Results indicated that, overall, actors provided higher control judgments than did observers, and both actual contingency and success influenced judged control. Type A and B actors did not differ in their self-perceptions of control but observers judged the Type A actors to have exerted more control than the Type B actors, primarily on positive contingency tasks. These findings suggest that Type As, because of their more active, dynamic style, may be credited by observers with more control or competence than is warranted. By contrast, the more relaxed style of the Type B may lead to lower than warranted evaluations of control or competence. Lastly, Type As were found to learn the contingencies better than Type Bs with important implications for the actual exercise of control.     

Effects of asynchrony on symmetry perception

The effect of temporal image segmentation on symmetry perception was investigated by means of stimuli composed of one part surrounding another. The two parts could be presented synchronously or with a temporal offset (20–100 ms), and each part could be either symmetrical or random. The task was to discriminate completely symmetrical (S) stimuli (in Experiment 1) or completely random (R) stimuli (in Experiment 2) from partially symmetrical (PS) stimuli in which one part was symmetrical and the other random. The R stimuli showed an asynchrony effect but the S stimuli did not. Furthermore, in both experiments, the PS stimuli showed an asynchrony effect when the symmetrical part was presented last but not when the symmetrical part was presented first (independent of whether it was the surrounded part or the surrounding part). Both results suggest that symmetry is strong enough to override this kind of temporal image segmentation.     

Neural substrate for brain stimulation reward in the rat: cathodal and anodal strength-duration properties.

The trade-off between current strength and duration of a stimulating pulse was studied for the rewarding and priming effects of brain stimulation reward (BSR). With cathodal pulses, strenght-duration functions for BSR had chronaxies of .8-3 msec. No differences were observed between the results for rewarding and priming effects. With anodal pulses. strength-duration curves were parallel to the cathodal curves at pulse durations of .1-5 msec, but at pulse durations greater than 5 msec the anodal curves showed a greater drop in required current intensity than did the cathodal curves. The parallel portion of the anodal curves was interpreted as due to anode-make excitation, and the drop at longer pulse durations was interpreted as due to anode-break excitation. Cathodal strength-duration functions for the motor effect elicited through the BSR electrodes had chronaxies of .15-.48 msec. Measurements of the latency of the muscle twitch confirmed that anode-make and anode-break excitation occurred, the latter becoming evident at pulse durations as brief as .3-.4 msec. The results provide quantitative characterization of cathodal and anodal strength-duration properties of the neural substrate for BSR and are discussed in terms of their value in guiding electrophysiological investigation of that substrate.     

Causal capture: contextual effects on the perception of collision events

In addition to perceiving the colors, shapes, and motions of objects, observers can perceive higher–level properties of visual events. One such property is causation, as when an observer sees one object cause another object to move by colliding with it. We report a striking new type of contextual effect on the perception of such collision events. Consider an object (A) that moves toward a stationary object (B) until they are adjacent, at which point A stops and B starts moving along the same path. Such "launches" are perceived in terms beyond these kinematics: As noted in Michotte's classic studies, observers perceive A as being the cause of B's motion. When A and B fully overlap before B's motion, however, observers often see this test event as a completely noncausal "pass": One object remains stationary while another passes over it. When a distinct launch event occurs nearby, however, the test event is "captured": It too is now irresistibly seen as causal. For this causal capture to occur, the context event need be present for only 50 ms surrounding the "impact," but capture is destroyed by only 200 ms of temporal asynchrony between the two events. We report a study of such cases, and others, that help define the rules that the visual system uses to construct percepts of seemingly high–level properties like causation.     

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.     

Conceptual combinations and relational contexts in free association and in priming in lexical decision and naming

Words known to have strong associates of a particular relational type were embedded in lists of other words with relations of the same type or in lists of words with relations of a different type (e.g.close-far in a list of other opposite pairs or in a list of synonym pairs). In free association, the probability of a response consistent with the relational context was higher than the probability of a response inconsistent with the context. In lexical decision and naming, significant priming was obtained for related pairs of words only when their relation was consistent with the relational context of the list in which they were embedded. The priming effects were obtained when the stimulus onset asynchrony between prime and target words was short (250 msec for lexical decision and 300 msec for naming), indicating that the effects were due to automatic retrieval processes. These findings point to the importance of the particular relations between words in the retrieval of information from memory, an aspect of processing overlooked by current memory models.     

Comparison of the effect of onset asynchrony on auditory grouping in pitch matching and vowel identification

Previous experiments have shown that when a slightly mistuned harmonic of a complex tone starts more than about 80 msec before the remaining components, it makes a reduced contribution to the pitch of the complex. This contribution decreases to zero by about 300-msec onset asynchrony. In vowel perception, however, analogous experiments have shown that a much shorter asynchrony (around 40 msec) is enough to ensure that a component does not influence a vowel’s phonemic category. The three experiments reported here demonstrate that this difference in the utility of onset time as a grouping cue does not arise because of differences in stimulus structure, but rather is due to the perceptual task. They show that the onset asynchrony needed in a pitch-matching experiment to remove the contribution that a mistuned component makes to the pitch of a vowel is the same as that needed to remove the contribution to the pitch of a flat-spectrum complex tone. They further show that a much smaller onset asynchrony is needed to perceptually remove the same harmonic from a vowel for the calculation of vowel quality. The implication of this result for models of auditory grouping is discussed.