Discrimination of time intervals bounded by tone bursts

Trained listeners had to discriminate, in a four-level 2AFC paradigm, the duration of a time interval bounded by pairs of brief tone bursts. The time intervals ranged from 10 to 100 msec. When the tone-burst markers were similar in their intensity (86 dB SPL) and frequency (1 kHz), the just noticeable time difference was found to be monotonically related to the base interval. On the other hand, when the intensity of the first marker was severely attenuated (by 50 dB) or when a large (2-octave) difference was introduced between the frequencies of the two markers, the time discrimination functions became nonmonotonic. A similar, albeit slight, departure from monotonicity was also achieved by making the second marker much longer than the first (300 msec vs. 10 msec). The nonmonotonicity of these time discrimination functions is compared to the well-documented nonmonotonicity that may be observed for voice onset time (VOT) discrimination functions.     

Discriminating time intervals presented in sequences marked by visual signals.

This article presents the results of three experiments on the discrimination of time intervals presented in sequences marked by brief visual signals. In Experiment 1A (continuous condition), the participants had to indicate whether, in a series of 2-4 intervals marked by 3-5 visual signals, the last interval was shorter or longer than the previous one(s). In Experiment 1B (discontinuous condition), the participants indicated whether, in a presentation of two series of 1-3 intervals, with each series being marked by 2-4 signals, the intervals of the second sequence were shorter or longer than those of the first. Whenever one, two, or three standard intervals were presented, the difference threshold was as high at 150 msec as it was at 300 msec with the continuous method but increased monotonically from 150 to 900 msec with the discontinuous method. With both methods, the increase was well described by Weber's law--the Weber fraction was roughly constant--between 600 and 900 msec (Experiment 2), whereas between 900 and 1,200 msec (Experiment 3), the Weber fraction increased.     

Discriminating time intervals presented in sequences marked by visual signals

This article presents the results of three experiments on the discrimination of time intervals presented in sequences marked by brief visual signals. In Experiment 1A (continuous condition), the participants had to indicate whether, in a series of 2–4 intervals marked by 3–5 visual signals, the last interval was shorter or longer than the previous one(s). In Experiment 1B (discontinuous condition), the participants indicated whether, in a presentation of two series of 1–3 intervals, with each series being marked by 2–4 signals, the intervals of the second sequence were shorter or longer than those of the first. Whenever one, two, or three standard intervals were presented, the difference threshold was as high at 150 msec as it was at 300 msec with the continuous method but increased monotonically from 150 to 900 msec with the discontinuous method. With both methods, the increase was well described by Weber’s law&#x2014the Weber fraction was roughly constant&#x2014between 600 and 900 msec (Experiment 2), whereas between 900 and 1,200 msec (Experiment 3), the Weber fraction increased.     

Reflex inhibition in humans: Sensitivity to brief silent periods in white noise

A white noise (60 dB SPL) was always present except for brief silent periods (“gaps”) which occurred just before an eyelid reflex was elicited in human volunteers by a brief innocuous shock to the forehead. In Experiment 1 (n=8), 10-msec gaps (“S1”) were given 40, 80, 120, 160, or 200 msec before the shock (“S2”). Compared with S2-alone trials, the reflex was inhibited by about 50% at intervals of 80 msec and beyond. Experiment 2 (n=12) first provided detection thresholds for gaps using a simple version of the method of limits: on average a gap of 5.4 msec duration was just detected. Then gaps of 0, 2, 4, 6, 8, and 10 msec were given in random order, each 100 msec before S2. The 4-msec stimulus was an effective inhibitor of the reflex, and inhibition further increased on to 6- and then to 8-msec durations. A comparison of the values obtained on reflex inhibition with the 5.4-msec threshold obtained with the conventional psycho-physical test reveals that in humans reflex inhibition provides an objective index of stimulus detection that is at least of sufficient sensitivity to warrant its clinical application. The steady increase in reflex inhibition as gap duration increased from 2 to 8 msec may be of significance for tracing the rate of decay of afferent stimulation following noise offset, as it presumably reflects the growing sensitivity to the resumption of the noise as the duration of the silent period is increased.     

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.     

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.     

Visual temporal integration and simple reaction time

Intensity-time reciprocity for simple RT to foveal pulses of light was demonstrated up to 11 msec by using two experimental paradigms. The first paradigm was designed to separate two possibly confounded factors displayed by previous studies investigating the effects of increased stimulus duration on RT: (1) an asymptotic RT as a function of the increasing energy of a pulse as its duration is increased, and (2) the breakdown of integration as the pulse duration is increased. The second paradigm was designed to avoid the first factor so as to maximize the possibility of finding partial integration at long durations. In this paradigm, partial integration was demonstrated for additional light input presented as long as 64 msec after stimulus onset. The failure of other studies to demonstrate temporal integration for RT is discussed in terms of these paradigms.     

Information encoding in short firing rate epochs by single neurons in the primate temporal visual cortex

Abstract

The information available about face identity from the firing rate and from temporal encoding in the spike train of single neurons recorded in the temporal lobe visual cortical areas of rhesus macaques was analysed using principal component and information theory analyses of smoothed spike trains. The neurons analysed had responses selective for faces. The stimulus set consisted of 20 different faces. The first principal component provided by a considerable extent the most information (57%) available in principal components 1–5, with the second adding 18%, the third 16%, and the fourth and fifth adding 9%. For each image, the weighting on the first principal component was highly correlated with the mean firing rate of the neuron to that image. The information available from the firing rate of the neuron was very close to that available in the first principal component. Information theory analysis showed that in short epochs (e.g. 50 msec) the information available from the firing rate can be as high, on average, as 65% of that available from the firing rate calculated over 400 msec, and 38% of that available from principal components 1–3 in the 400-msec period. It was also found that 30% of the information calculated from the first three principal components is available in the firing rates calculated over epochs as short as 20 msec. More information was available near the start of the neuronal response, and the information available from short epochs became less later in the neuronal response. Taken together, these analyses provide evidence that a short period of firing taken close to the start of the neuronal response provides a reasonable proportion of the total information that would be available if a long period of neuronal firing (e.g. 400 msec) were utilized to extract it, even if temporal encoding were used. The implications of these and related findings are that at least for rapid object recognition, each cortical stage provides information to the next in a short period of 20–50 msec, does not rely on temporal encoding, and completes sufficient computation to provide an output to the next stage in this same 20- to 50-msec period.     

Tests of a two-stage model of visual matching

Predictions from a model of visual matching were tested in two experiments. The model consists of a wholistic comparison process followed by an element-by-element comparison process. All stimuli are processed by the first stage but only those that permit a decision based on a wholistic comparison produce responses. When discrimination is difficult and a decision cannot be reached by a wholistic comparison, the second stage of processing is initiated. Degree of discriminability and stimulus duration (100 and 1000 msec.) were varied in both experiments. In Exp. 1, the stimulus elements were arranged in a square configuration to facilitate a wholistic comparison. As predicted, the hard-different stimuli took longer to match than the same or easy-different stimuli. The hard-different stimuli presented for 1000 msec. took longer to match than those presented for 100 msec. There was no difference in accuracy between responses to hard-different pairs at the two durations. In Exp. 2, the stimulus elements were arranged in a horizontal row and placed one above the other to facilitate element-by-element comparison. As predicted, these stimuli produced slower and more accurate responses for same and hard-different stimulus pairs only when they were exposed for 1000 msec. Responses to easy-different stimulus pairs were made quickly and accurately.     

On the distinction between sensory storage and short-term visual memory

A pattern made by randomly filling cells in a square matrix was presented for 1 see and followed, after various intervals, by an identical or similar pattern. Ss responded “same” or “different.” Performance was fast and accurate if the interval was short and there was no movement or masking of the pattern during the interval. Performance was slower, less accurate, and highly dependent on pattern complexity if the interval exceeded 100 msec or if there was movement or masking. The results are interpreted as evidence for two distinct classes of visual memory: high-capacity sensory storage which is tied to spatial position and is maskable and brief; and schematic short-term visual memory which is not tied to spatial position, which is protected against masking, and which becomes less effective over the first few seconds but not over the first 600 msec.     

Concurrence costs in double stimulation tasks

Seven experiments are described on reaction time (RT₁) to a first auditory stimulus in a double stimulation paradigm, where the response to a second visual stimulus was explicitly non-speeded. In all studies it was found that, compared to a single stimulus control condition, RT₁ showed a constant delay of about 20–30 msec. The effect occurred irrespective of (a) the viewing conditions of the second stimulus in terms of either duration, processing demands or presence vs absence of a backward masking signal (experiments 1, 4, 5, 6, 7); (b) the duration of the interstimulus interval ranging from -200 msec up to at least a second (experiments 2, 3, 5); and (c) the processing demands of the first task (experiment 7). It is suggested that the delay reflects a basic concurrence cost which remains when two reactions can be time-shared.     

The slow formation of a pitch percept beyond the ending time of a short tone burst

The discriminability of short tone bursts differing in frequency was measured in terms of the sensitivity index d' as a function of interstimulus interval (ISI). The two stimuli presented on each trial consisted of either 6 or 30 sinusoidal cycles. When the frequency of the first stimulus varied randomly and widely from trial to trial (Experiment 1), discriminability was maximal for an ISI of about 400 msec in the 6-cycles condition and for a significantly longer ISI (of about 1 sec) in the 30-cycles condition. However, when the first stimulus had only two possible frequencies and the second stimulus was fixed (Experiment 2), the optimal ISI appeared to be about 400 msec in both conditions. A final experiment confirmed that, for tone bursts of 30 cycles, the optimal ISI was dependent on the perceptual uncertainty of the first stimulus. These results support the idea that the duration required to perceive the pitch of a sound as accurately as possible may far exceed the duration of the stimulus itself. More importantly, they indicate that the required duration is not a constant.     

Stroboscope motion: Effects of duration and interval1

The quality of stroboscope motion induced by the successive presentation of two illuminated squares obeys two rules. For all stimulus durations shorter than 100 msec, optimal motion occurs when the stimulus onsets differ by about 120 msec. For stimulus durations longer than 100 msec, optimal motion occurs when the second stimulus begins at the termination of the first stimulus. The two rules relating quality of motion to duration suggest a single principle, namely, that the quality depends only on the interval between the visual responses to the two stimuli. The interresponse interval at which motion is optimal is independent of stimulus duration.     

Timing the shift in retinal local signs that accompanies a saccadic eye movement

Thephantom array was used to probe the time course of the shift in retinal local signs that accompanies a saccadic eye movement. The phantom array materializes when one saccades in the dark across a point light source blinking 120 times per second. One sees a stationary array of flashes—the first materializes discretely near the intended endpoint of the saccade, and subsequent flashes materialize progressively closer to the actual position of the blinking light. Four trained observers indicated the perceived location, relative to the phantom array, of a 1-msec marker flash (M) produced by two LEDs (light-emitting diodes) that vertically bracketed the blinking light. The marker was seen as spatially coincident with the first flash when it flashed 80 to 0 msec before the saccade, and was seen as spatially coincident with either the first flash or the actual position of the blinking light when it flashed mare than 80 msec before the saccade, indicating, respectively, that the shaft is presaccadic and rather abrupt.     

Identification and pronunciation effects in a verbal reaction time task for words,pseudowords, and letters

The question addressed in this investigation was whether faster reading and pronunciation of words than orthographically regular pseudowords is due to faster identification or to faster programming and execution of the motor response. In Experiment I, three different response conditions (naming, threechoice signaled responding, and one-choice signaled responding) were employed to separate the identification and articulation processes in a verbal reaction time task. It was found that, for all intents and purposes, single, isolated letters are processed as if they were very short words. Words are read and pronounced 72 msec faster than pseudowords. Words are also pronounced 30 msec faster than pseudowords even if the reader has longer than 1 sec to identify the stimulus (three-choice condition) or to both identify the stimulus and preprogram the response (one-choice condition). The data indicate that words are identified about 52 msec faster and articulated about 30 msec faster than pseudowords. Since the number of response alternatives (one or three) does not interact with stimulus type (letter, word, or pseudoword) in the signaled response control condition, the 30-msec difference is due to response execution and not to differential response programming. Response programming takes in the neighborhood of 236 msec. Experiment 2 investigated the effect of local orthographic context upon the identification of the first letter of a string of letters. No difference was found in identifying the initial letter of words and pseudowords, but the initial letter of these orthographically regular letter strings was identified and named 10 msec faster than the initial letter of orthographically anomalous strings of letters (anagrams). The data from the two experiments are supportive of theories of reading that assume (1) that the letters of visually presented words are processed simultaneously, in parallel, (2) that there is a relatively direct access and retrieval of the phonological memory codes for the names of words, and (3) that orthographically regular pseudowords having no representation in the phonological lexicon undergo a grapheme-to-phoneme transformation that takes longer to finish than the direct spelling-to-sound process used for words.     

Suitability of the IBM XT,AT, and PS/2 keyboard,mouse, and game port as response devices in reaction time paradigms

The IBM PC keyboard is a convenient response panel for subjects in a reaction time task when the stimuli are presented on the same machine. However, there is a mean delay of about 10 msec and a random error of ±7.5 msec (±5 msec on the AT or PS/2). Our analyses show that for typical single response experimental situations, this added variance is acceptable. With mouse buttons, timing resulted in a delay of 31 ±2 msec if the mouse ball was steady but 45 ±15 msec if it was moving, and a 25-msec refractory period before a second response could be detected. With keys connected to the game port, timing was accurate to 1 msec. For timing the interval between two nearly simultaneous responses, only the game port method is recommended. Any research application should provide an external check on reaction timing accuracy and should correct any mean error.     

Immediate and delayed recognition of sequentially presented random shapes.

Two experiments tested whether short-term memory accounts for the recency effect observed with rapid sequential presentation of nonverbal stimuli. Four random shapes were presented sequentially (with no interstimulus interval) on each trial at rates of 150 msec, 250 msec, 500 msec, and 1,000 msec per stimulus. Subsequent recognition varied positively with exposure duration, ranging from 57% at 150 msec to 77% at 1,000 msec. Two serial position effects were observed: a slight decrease in recognition accuracy for the first stimulus in each sequence and a large increase in recognition for the last stimulus in each sequence. The recency effect was not altered by an intervening 30-sec delay, an intervening 30-sec copying task, or an intervening 30-sec copying and counting task. Since neither visual nor verbal distractors altered recognition accuracy, it was suggested that all shapes were processed directly into long-term memory storage. It also was hypothesized that long-term storage of a nonverbal stimulus requires identification of a distinctive feature of the stimulus and that this process may continue for a brief period after actual stimulus offset.     

Event-related brain potentials: report order and task switch on multidimensional stimuli identification

An experiment was conducted to evaluate the effect of order of reporting stimulus dimension in multidimensional stimulus identification using a switch-task paradigm. Participants were required to identify each two-dimensional symbol by pushing the corresponding buttons on the keypad on which there were two columns representing the two dimensions, part and shape. The two orders of report were Order Part/Shape and Order Shape/Part. There was a task cue prior to each presentation of a symbol indicating the particular report order the participants should perform. The cue changed randomly. Both behavioral data and event-related potentials were recorded from 12 college students. Analysis of behavioral data showed switch cost indicated by increase in response time was greater for Order Shape/Part, a less appropriate order of reporting dimensional values, than Order Part/Shape (88 msec. vs 9 msec. for response time for the first stimulus dimension; 96 msec. vs -1 msec. for response time total). Neural activities under Order Shape/Part and Order Part/Shape were different, and it seems plausible that participants put more effort into selection and showed more related semantic activation in Order Shape/Part than in Order Part/ Shape which fits the Chinese adjective-then-noun language habit.     

Information processing of letter and word pairs as a function of on and off times

The present study seeks to extend a provisional model of visual information processing with sequential inputs currently under development, employing a computer-based cathode-ray tube display system. Letter and word pairs were presented for 28 different on-off time combinations with on times ranging from 5 msec to 50 msec and off times ranging from 1 msec to 125 msec. The results suggest that both on, off, and total processing times affect per cent correct detections, and that while a gradual increase in per cent correct detections occurs up to about 50 msec of total processing time, a marked discontinuity appears to occur approximately between 50 and 60 msec of total processing time, with per cent correct detections jumping abruptly from about 40% correct detections to about 90% correct detections over a total processing time span of only 10 msec.     

IDENTIFICATION OF BRIEF PRESENTATIONS OF FACIAL EXPRESSIONS OF AFFECTS IN SCHIZOPHRENICS

Two experiments were designed to test information extraction capacity from briefly shown photographs depicting simple familiar objects and facial/affective stimuli. Photographs were presented tachistoscopically at six exposure times, 1 sec, 200 msec, 40 msec, 20 msec, 4 msec, 2 msec, to chronic schizophrenic patients, general medical patients, and nonpatient control subjects. Experiment 1 was conducted using the number of correct responses (true scores) and experiment 2 using the number of trials taken (error scores) to identify the target stimuli, as the dependent measures. In experiment 1, schizophrenics did not differ from general medical patients but both were inferior to nonpatient controls in identifying brief visual stimuli. However, in experiment 2, schizophrenics required significantly more trials than general medical patients, who in turn required significantly more trials than nonpatient controls in identifying brief visual stimuli.