Retention of time information in forced-choice duration discrimination

We explore the effect on performance in a forced-choice duration-discrimination task of varying the interstimulus interval (ISI) from 0 to 2 sec. The durations were brief empty intervals (115–285 msec) bounded by very brief auditory pulses. Performance improved as the ISI increased from 0 to 1/2 sec, but a further increase in ISI up to 2 sec resulted in little further change in performance. The “time information” derived from a brief interval bounded by auditory pulses does not appear to be susceptible to the very short-term perceptual memory loss inferred in other auditory discriminations.     

Extinction of Sidman avoidance behavior

Extinction of Sidman avoidance behavior by eliminating the noxious stimulus was studied in Sprague-Dawley rats with bar-pressing as the response. Each of three subjects was trained and extinguished on each of the following schedules in a different order: nondiscriminated, response-shock interval = 20 sec, shock-shock interval = 5 sec; nondiscriminated, response-shock interval = 40 sec, shock-shock interval = 5 sec; discriminated, response-white noise interval = 15 sec, noise-shock interval = 5 sec, shock-shock interval = 5 sec. Less than one 4-hr session was required for extinction for all procedures. When a warning stimulus was present, resistance to extinction increased. Subjects did not, however, respond to avoid the signal. Only small differences in extinction were found after training on different schedules with no warning signal.     

Changes in threshold level produced by a signal preceding or following the threshold stimulus

In a previous experiment (Howarth and Treisman, 1958) it was shown that when a warning preceded a stimulus by a fixed interval, the threshold level for the stimulus was higher the longer the fixed interval. A model of this effect was proposed, assuming that the threshold criterion adopted by the subject at any moment was modified by his estimate of the probability of a stimulus at that moment.

Three predictions are derived and tested. It is found that: the standard deviation of the response is constant despite the shifts in threshold induced; the threshold continues to fall as the interval from warning to stimulus is decreased to zero, with the lowest threshold when the warning signal and the stimulus are simultaneous; and that a warning signal following the stimulus by an interval of less than 0 5 to 1 sec. also lowers the threshold.     

Effect of interval between auditory and preceding visual stimuli on auditory sensitivity

Auditory thresholds were determined by a modified method of limits, in introverts, ambiverts and extraverts, under three intensities of light. Five determinations were made: one before, one during and three (30 sec., c. 8 and 16 min.) after the light stimulation. An analysis of variance of the data showed significant results for the interval conditions, the personality type and the interaction of these parameters, under the weak light. Interval effects were also significant under medium and strong light. A weak light increased, and a strong light decreased, auditory sensitivity when threshold determinations began 30 sec., but not more than about 8 min., after the light stimulation, in introverts.     

Interval patterning and auditory gap detection

Pattern effects associated with the perception of the temporal microstructure of auditory signals were examined. Temporal changes, or gaps, were introduced into auditory interval patterns produced by a sequence of pulses. Discrimination thresholds for positive, and for negative, gaps were obtained as a function of the surrounding pattern of intervals. Gap thresholds increase with the slope of the surrounding interval pattern. Gap thresholds are smaller when the gap interval represents an extension, rather than a reversal, of the surrounding pattern. The results are in agreement with Heise and Miller’s thresholds of tonal isolation from repeated melodies, and with Mangelsdorf’s visual extrapolation thresholds of point-of-collision. The agreement of results from diverse test situations suggests a non-specifiC., general patterning effect upon discontinuity thresholds.     

Aging and temporal discrimination of brief auditory intervals

Summary In a duration-discrimination experiment, young adults (mean age = 25.1), middle-aged adults (mean age = 45.5), and older adults (mean age = 64.6) were presented with two very brief auditorily marked intervals per trial, and their task was to decide which of the two was longer in duration. An adaptive psychophysical procedure was used to determine difference thresholds in relation to a constant standard interval of 50 ms. It was found that duration-discrimination performance was unaffected by age; all three age groups yielded a difference threshold of approximately 17 ms. It was concluded that the ability to discriminate durations of very brief auditory intervals appears to be based on an underlying timing mechanism that does not slow down with advancing adult age.     

Duration discrimination of empty and filled intervals marked by auditory and visual signals

Experiments 1 and 2 compared, with a single-stimulus procedure, the discrimination of filled and empty intervals in both auditory and visual modalities. In Experiment 1, in which intervals were about 250 msec, the discrimination was superior with empty intervals in both modalities. In Experiment 2, with intervals lasting about 50 msec, empty intervals showed superior performance with visual signals only. In Experiment 3, for the auditory modality at 250 msec, the discrimination was easier with empty intervals than with filled intervals with both the forced-choice (FC) and the single stimulus (SS) modes of presentation, and the discrimination was easier with the FC than with the SS method. Experiment 4, however, showed that at 50 and 250 msec, with a FC-adaptive procedure, there were no differences between filled and empty intervals in the auditory mode; the differences observed with the visual mode in Experiments 1 and 2 remained significant. Finally, Experiment 5 compared differential thresholds for four marker-type conditions, filled and empty intervals in the auditory and visual modes, for durations ranging from .125 to 4 sec. The results showed (1) that the differential threshold differences among marker types are important for short durations but decrease with longer durations, and (2) that a generalized Weber’s law generally holds for these conditions. The results as a whole are discussed in terms of timing mechanisms.     

Retroactive raising of a sensory threshold by a contralateral stimulus

In an experiment designed to extend Howarth and Treisman's recent observations on the lowering of the visual and auditory threshold produced by a warning stimulus, it has been found that the threshold to electrical stimulation of one forearm is raised by a similar stimulus on the other forearm. As in the earlier experiments the “warning” was effective if it came 100 millisec. before or after the threshold stimulus. The effect increased with increasing warning strength over the range of five near-threshold strengths used.

These results appear to be inconsistent with the explanation previously proposed to account for the retroactive lowering of threshold. This suggested that the warning was acting simply as a marker, reducing the subject's uncertainty as to when the stimulus was coming. The fact that the rise in threshold was also induced retroactively shows that some interaction must be occurring in the central processes concerned in perception, and that it cannot be explained in terms of attenuation of the afferent volley.     

Warned reaction times of sociopaths

A warned reaction time (RT) task was employed with eight male sociopaths and eight normal male Ss. A warning light appeared at a variable interval preceding a light to which the S responded with a key press. All Ss received both a regular and an irregular series with warning intervals of 1, 2, 4, 8, and 16 sec. In the regular series, blocks of intervals were presented in an ascending order. In the irregular series each interval followed every other interval equally often. Sociopaths obtained reliably slower RTs than did control Ss, showing a constant decrement across all intervals in the two kinds of series.     

Effect of information feedback on temporal discrimination in concurrent and post-feedback measures

College students estimated time intervals (5, 6, 7, 8, and 9 sec.) where one group (N = 20) received information feedback in terms of actual interval durations and a second group (N = 18) received no information. Theshold measures were then taken for all subjects using the method of constant stimuli (comparison stimuli of 5, 6, 7, 8, and 9 sec. and a 7-sec. standard). In addition to increased accuracy and consistency of judgments, the feedback group showed a decreasing Weber fraction during the estimation phase, while the Weber fraction for the no-feedback group increased. The feedback group retained only a slight advantage in subsequent threshold measures; group differences in difference thresholds and derived nonparametric estimates of d' were nonsignificant.     

Criterion shifts in the measurement of tactile masking

A series of experiments was conducted to determine the effects of method of threshold measurement on the amount of threshold shift produced by a masking stimulus. The amount of contralateral tactile masking of the fingertip was found to be much greater when thresholds were measured by the Békésy tracking method than when measured by a forced-choice method. When the Békésy tracking procedure was modified so that each observation interval containing a brief stimulus was followed almost immediately by a second observation interval not containing a stimulus, the amount of masking was substantially reduced for both contralateral tactile masking and auditorytactile masking and corresponded almost exactly with the amount of masking measured by the forced-choice method. No such reduction in the amount of masking was obtained by using this procedure to measure ipsilateral tactile masking or auditory masking.     

Signal functions in discriminated avoidance behavior

Four rats were trained to lever press under a discriminated avoidance/escape schedule in which separately signalled safe and warning periods were 100 sec and 32 sec respectively. The auditory and not the visual component of the compound warning signal became associated with the discriminative control of lever pressing. Avoidance behavior also came under temporal control, in that the probability of lever pressing increased as the warning period progressed. Timing began with the onset of the warning signal rather than the offset of the safe signal. However, after the warning signal had been progressively eliminated, timing began with the offset of the safe signal. When neither signal was normally available, the temporal distribution of avoidance behavior changed markedly. Drifts in the temporal distribution of lever pressing occurred throughout the study; these were manipulated for two animals.     

Rapid acquisition of discrete-trial lever-press avoidance: effects of signal-shock interval

Acquisition of discrete-trial lever-press avoidance learning was studied in three experiments. Experiment I compared a new training procedure, which produces rates of lever-press avoidance learning comparable to those obtained in shuttle boxes, with a “conventional”, less efficient training procedure. A factorial design was used to compare continuous versus intermittent shock and a long-variable versus a short-fixed signal-shock interval. Learning was best in the groups trained with the long and variable interval and poorest in those trained with the short and fixed interval. Type of shock had no effect. Experiment II separated the effects of duration from those of variability of the signal-shock interval. Fixed and variable intervals of 10 and 60 sec were tested and duration was the only significant factor. Experiment III addressed the effect of the differential opportunity to avoid provided by long signal-shock intervals by varying this interval from 10 to 60 sec in 10-sec steps. Only the 10-sec group showed slow acquisition relative to the others. Analysis of avoidance response latencies showed that the distributions for all groups were positively skewed and that skewness increased with increasing duration of the signal-shock interval. At intervals longer than 20 sec, the animals made progressively less use of their increased opportunity to respond. The data do not support the opportunity-to-respond interpretation of the effects of duration of signal-shock interval and suggest that some type of inhibitory process may block lever-press avoidance learning at intervals as short as 10 sec. The significance of these findings for species-specific defense reaction and preparedness theories was emphasized.     

Two temporal parameters of food postponement

Rats were trained to press a lever under schedules of food postponement. In the absence of lever presses, food was delivered periodically (food-food interval). Responses initiated a second interval (response-food interval) that was reset by each additional response. Performance was first studied at different response-food intervals with the food-food interval fixed at 30 or 60 sec, or 10 min. Response-food intervals were examined in ascending order and then recovery was studied at shorter intervals. Finally, the food-food interval was manipulated with response-food interval fixed at 30 sec. At food-food intervals of 30 and 60 sec, responding first increased and then decreased as the response-food interval increased. At the 10-min food-food interval, responding decreased with increasing response-food interval. In general, very low rates of responding occurred when the response-food interval was 60 sec or more and when it equalled or exceeded the food-food interval. However, responding was maintained in one animal when the food-food interval was decreased from 120 to 15 sec with the response-food interval at 30 sec. Results, in terms of several dependent variables, are compared with data on shock avoidance. Effects of response-independent and response-produced food and shock are discussed.     

Influence of auditory or visual warning on visual reaction time with variations of subjects' alertness

The purpose of the study was to determine the effect of visual and auditory warning on visual reaction time with variations of subjects' alertness. An experimental group of 30 subjects was tested with an auditory or visual warning signal; foreperiods lasted 3, 2, and 4 sec. Reaction time was shorter as alertness improved and with an auditory warning signal. Comparable measures in a control group showed that visual reaction time was shorter when an auditory warning signal was used.     

Perfect visual short-term memory for periodic patterns

Abstract

The short-term memory for spatial frequency information was assessed by measuring the spatial frequency discrimination thresholds for briefly flashed luminance gratings as a function of the time interval between the test and reference gratings, using a computer-controlled two-interval forced-choice procedure. Discrimination thresholds were stable for interstimulus intervals in the range 1–30 sec under all conditions tested. At low contrasts, short exposure times and low spatial frequencies discrimination thresholds increased, but no interactions between stimulus parameters affecting thresholds and interstimulus interval were observed. It is concluded that factors limiting spatial discrimination are associated with the sensory coding stage. Spatial discrimination and visual memory may be based on a common representation, which is perfectly retained in short-term memory. Visual half-field tests revealed no hemispheric differences in the processing and retention of spatial frequency information.     

Aging effect on detectability,criticality and urgency under various auditory conditions

The objective of the study was to investigate the relationship between different components of an auditory warning signal and determine elderly driver’s detection, criticality and urgency perceptions under varied auditory warning conditions. A laboratory study was conducted involving 28 younger and 28 older adults. A pure-tone audiogram was administered for quantification of the participant’s hearing level (in dBHL) prior to the test protocols. Audiogram was conducted in a sound isolated booth. The main experiment investigated the effects of frequency, temporal characteristics, aging, and noise on detectability, caution and perceived urgent levels. Method of adjustment was used by the subjects to adjust the sound pressure level (dBA) till they detected, or felt caution or urgent. Overall, the results indicated that elderly had higher sound pressure threshold than younger individuals in all the sessions (i.e., detectability, caution and urgency). Elderly were found to have higher hearing thresholds especially at 4000 Hz. Higher frequencies were also seen to require less sound pressure thresholds to convey feeling of caution and urgency. Sound pressure threshold to convey the feeling of urgency was the lowest for 2000 Hz and 4000 Hz with 1000 Hz requiring the highest threshold intensity. In conclusion, current study findings suggest frequency, temporal and spectral components to influence a person’s criterion. We would recommend the use of complex tones (multi-components) having high frequency around 2000 Hz for detection, warning and urgent conditions.     

Stimulus control of avoidance behavior

The introduction of a warning signal preceding shocks greatly increased the effectiveness of avoidance responding. Periods of “warm-up” at the beginning of the session were eliminated, and the number of shocks received by the subjects was greatly reduced. With response-shock interval constant, response rate increased as the interval between the response and the onset of the warning signal was shortened. The response tended to occur shortly after the onset of the warning signal regardless of the duration of these “safe” periods. A greatly elevated response rate was maintained even when the duration of the safe period was reduced to 0.3 sec. Thus, the pre-shock signal obtained nearly exclusive control of the responding and overrode the usual “temporal discrimination” of the response-shock interval.     

Auditory threshold,signal-to-noise ratio and signal detection theory

The use of Signal Detection Theory has demonstrated that there is not an auditory threshold at the level supposed by classical psychophysics, but has not disproved the existence of an auditory threshold at a lower level. Following the recommended signal detection theory procedure fairly closely, an experiment obtained evidence either of the existence of a signal-to-noise ratio audi tory threshold, or a nonlinear relationship between stimulus and response which could not be statistically distiguished from such a threshold , Using the same apparatus and subjects, audi tory thresholds were also obtained using the classical method of limits. The acoustic pressure for the classical thresholds was about five times as great as for the signal detection theory method.     

The response-shock-shock-shock interval and unsignalled avoidance in goldfish

Goldfish were trained to swim back and forth in a shuttle tank to avoid unsignalled shocks. The response-shock interval and the shock-shock interval were always of equal duration; both were either 15, 30, 45, or 60 sec. Response rates varied inversely with response-shock–shock-shock interval duration, as has been found with rats. Percentage of shocks avoided was somewhat lower at the 15 sec response-shock–shock-shock interval, but otherwise did not vary systematically with changes in the interval. As the response-shock–shock-shock interval increased, the fish made increasingly more responses than necessary to avoid all shocks. Interresponse-time distributions showed that response probability rose to a maximum at about 15 to 25 sec after a response, regardless of the response-shock–shock-shock interval. Thus, at the longer intervals the fish were responding too early in the response-shock–shock-shock interval to minimize response rates.