Robert Efron

Hemispheric specialization of memory for visual hierarchical stimuli

Unilateral brain-damaged patients and normal control subjects were asked to remember visual hierarchical stimuli consisting of larger forms constructed from smaller forms. The right-hemisphere damaged patients made more errors in remembering the larger forms relative to the smaller forms, whereas the left-hemisphere damaged patients made more errors in remembering the smaller forms relative to the larger forms. These findings are discussed as they relate to hemispheric specialization for visuospatial processing.

The minimum duration of a perception

Abstract The time course of the perception of visual and auditory stimuli has been studied by means of an analysis of the temporal errors in the judgement of simultaneity of two stimuli. In the first experiment, the subject is required to report when the onsets of two stimuli (of different durations) are simultaneous. In the second experiment, the subject is required to report when the offset of one stimulus is simultaneous with the onset of the second stimulus. The results indicate that visual perceptions have a minimum duration which lies in the range of 120–240 msec, and that auditory perceptions have a minimum duration which lies in the range of 120–170 msec.

The relationship between the duration of a stimulus and the duration of a perception.

Abstract The time-course of the perception of visual and auditory stimuli has been studied by means of the analysis of the temporal errors in the judgement of the simultaneity of the offset of the first stimulus and the onset of the second stimulus in the same modality. The duration of the first stimulus is the independent variable and the magnitude of the subjects error is the dependent variable. The error analysis for the stimuli which were used indicates that both auditory and visual perceptions have a minimum duration, produced by stimuli of 120–130 msec or less, and that perceptions evoked by stimuli longer than this critical value are continuously graded with respect to duration. No evidence could be found to support the idea that perceptual durations are quantized in the temporal domain.

Effect of stimulus duration on perceptual onset and offset latencies

The effects of stimulus duration on perceptual onset and offset latency were compared in vision and audition. It was found that perceptual onset latency was independent of stimulus duration but that the perceptual offset latency was longer for brief stimuli than for stimuli that exceeded a critical duration. For stimuli longer than the critical duration, the perceptual onset and offset latencies were equal: The same temporal relationships were found in both modalities. The results indicate that for any specific stimulus parameters, reduction of stimulus duration results, ultimately, in a perception of fixed duration.

What is Perception

Perception is man’s primary form of cognitive contact with the world around him. As all conceptual knowledge is based upon or derived from this primary form of awareness, the study of perception has always had a unique significance for philosophy and science.

THE DURATION OF THE PRESENT

A star, two million light years distant from the earth, which exploded two million years ago, is experienced as exploding “now” by an observer on earth. Similarly, an electric shock, delivered to our great toe and experienced by us “now,” was actually given at least 25 milliseconds previously. From these two examples of the use of the word “now,” we see that it refers to the first moment of awareness of an event or an entity by a particular observer who is located in a unique position in the universe. “Now” is a term tha t refers, therefore, to an aspect of the experience of existence. This aspect of our experience is implicit in the very state of awareness and in every state of awareness. T o he conscious is to be aware of something now. T o be aware of nothing now, is to be unconscious. The “present” is a less precise term which refers to the period of time during which we are aware of an event or an entity.* The phrase, “the duration of the present,” within the context of an analysis of perception, refers t o the duration of a state of awareness of an object of perception, that is to say, the duration of a perception. The duration of a perception, i.e., the duration of the mental state, should not be confused with the duration of the physical stimulus which gives rise to it. The two durations are not necessarily identical. A physical stimulus may be presented to a subject for several seconds. By virtue of changes in attention within that period, several different perceptions may occur. Conversely, the

Conservation of temporal information by perceptual systems

Experiments in the auditory, visual, and vibratory modality employed two brief discriminably different stimuli, which were presented with temporal asynchronies unequivocally below the Hirsh-Sherrick threshold for performing temporal order judgments. A pair of such stimuli, experienced as a unitary perceptual event, is referred to as a “micropattern” composed of two “stimulus elements.” Ss could readily distinguish between two such micropatterns in which the temporal order of the stimulus elements was reversed. The discrimination was based on the perceptual dominance of the second stimulus element of each micropattern. This perceptual dominance was studied as a function of stimulus-element onset and offset asynchrony, the duration and intensity of the stimulus elements, and the difference (in frequency or wavelength) between the stimulus elements of a micropattern. The results suggest the existence of an operation of all perceptual systems in the time domain that acts to conserve information concerning the temporal order of the two stimulus elements at the expense of discriminatory acuity of the f’~rst element.

Detectability gradients as a function of target location

We examined the ability to detect a specified visual pattern (a target) in a randomly selected location when it was briefly presented with 11 other spatially distributed nontarget patterns and also when it was presented by itself for the same duration (50 msec) on a background of visual noise. Two experiments were designed to measure target detectability as a function of its location in the visual field where all possible target locations were equidistant from the fovea. A right visual field detection superiority was obtained in both experiments. In addition, highly significant detectability differences were observed within the right and left visual fields in both experiments. The origin of these detectability differences are interpreted in terms of parallel and serial processing mechanisms.

An ear asymmetry for gap detection following anterior temporal lobectomy.

A threshold elevation in the performance of auditory temporal order judgment in man has been reported in the ear contralateral to the side of an anterior temporal lobectomy. On the basis of temporal order judgments alone it is not possible to determine whether the deficit is attributable to an impairment of recognition, identification, or temporal resolution. The present monaural experiments compared the performance of the two ears in the detection of a gap in a broad-band noise burst in normal and temporal lobectomized subjects. The results revealed a right-left symmetry in gap detection performance by normal subjects but a significant deficit in gap detection in the ear contralateral to the side of an anterior temporal lobectomy--a finding interpreted as revealing the existence of a bonafide deficit in auditory temporal resolution induced by such resection.

Temporal ordering deficits following anterior temporal lobectomy

Abstract Subjects were required to report the pitch sequence of two 10-msec tones of different frequency presented monaurally while the stimulus onset asynchrony (SOA) between the two tones was varied. The value of the SOA at which the subjects achieved an 80% correct sequence report was determined by an adaptive procedure without feedback. This measure was compared in the right and left ears, on subjects with a right or left anterior temporal lobectomy and on a normal control group. The results reveal an elevated threshold for performing temporal order judgments in the ear contralateral to the surgical lesion.