Movement detection thresholds and stimulus duration

Movement detection thresholds were measured for varying exposures of a moving spot. A tradeoff was found in which an increase in duration (T) was offset by a decrease in the velocity required for detection (V). In the range of durations studied (about 50–700 msec), V × T was constant. The V × T constancy was interpreted in terms of the direct detection of movement as motion, and a comparison was made with Bloch’s law.     

Effect of stimulus intensity on lingual vibrotactile fusion thresholds

Lingual fusion thresholds for a two-pulse stimulus were obtained at a 15-dB sensation level and a 35-dB sensation level for 15 subjects (18 to 22 yr.). The 35-dB sensation level provided better temporal resolution thresholds as well as less variable responses.     

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.     

Overshadowing and stimulus duration

In 3 experiments, the authors investigated the effect of stimulus duration on overshadowing. Experiments 1 and 2 examined responding to a target conditioned stimulus (CS1) when it was conditioned in compound with a coterminating overshadowing stimulus (CS2) that was longer, shorter, or of the same duration (the long, short, and matched groups, respectively). Equal overshadowing of conditioning to CS1 was obtained in all 3 conditions relative to a control group conditioned to the light alone. There were, however, differences in responding to CS2 as a function of its absolute duration. Experiment 3 examined the contribution of the food-food interval/CS onset-food interval ratio to these findings. In Experiments 1 and 2, the ratio differed for the overshadowing CS but not for the target CS. In Experiment 3, this arrangement was reversed, but the pattern of results remained the same. The implications of these findings for trial-based and real-time models of conditioning are discussed.     

Intervening stimulus effects on category judgments of duration

Auditory pulses (1,000 Hz) occurring between the 500-Hz bounding markers of durations being judged were varied in their position and number over three experiments which examined the effects of these factors on measures of amount of filled-duration illusion (FDI) and interduration discriminability. The results establish that the locus of the FDI is postattentive, since some of the incoming sensory information, selected on the basis of simple physical cues, can be excluded from further processing. FDI decreases both when the intervening stimuli come from a different source (earphone channel) to the marker stimuli and when they appear as part of an ongoing sequence of background pulses. Discrimination of durations containing intervening stimuli is enhanced if the filler events are placed such that repetitions of a given subinterval result. Thomas and Brown’s (1974) “chunking” model can account for the observed effects with the additional assumption that the error associated with encoding a given subinterval is sequentially modified as a function of number of recent encodings.     

Control of responding by stimulus duration

Pigeons were trained on a procedure in which the key was white for 30 sec, alternating with periods of darkness, or timeout. In a nondifferential training procedure, timeout duration was held constant at either 9 or 21 sec for different animals, and pecks on the white key were reinforced on a variable-interval 36-sec schedule. After 30 sessions an extinction generalization test was conducted where the duration of the timeout was varied from 3 to 27 sec. This test showed no differences in responding following timeouts of different durations. In a differential training procedure, timeout durations of either 9 or 21 sec were randomly scheduled for each animal. The variable-internal schedule was in effect following the same timeout duration as in the prior nondifferential procedure. No pecks were reinforced after the other timeout duration. In 40 sessions, differences in response rates following the two durations gradually developed. A maintained generalization procedure was then imposed in which timeout durations were varied from 3 to 27 sec, with the variable-interval schedule in effect following only the same duration as in the previous procedures. The first maintained generalization session showed that the prior differential training had established control of the animals' behavior by the timeout duration. In continued training on the maintained generalization procedure, control by the timeout duration decreased.     

Effects of stimulus duration and inter-letter spacing on letter-in-string identification

Effects of stimulus duration and inter-letter spacing were studied in a letter-in-string identification paradigm. Participants were shown strings of 5 random consonants (e.g., PGKDM) centered on fixation and were asked to identify the letter that had appeared at a post-cued location. Stimulus duration was manipulated in Experiment 1 (13 ms–91 ms), and inter-letter spacing manipulated in Experiment 2 (for a fixed stimulus duration of 26 ms). We contrasted performance to outer-letters (positions 1 and 5) with non-central inner letters (positions 2 and 4), the first-letter (position 1) with the final letter (position 5), and the central-letter (position 3) with the other inner letters (positions 2 and 4). The outer-letter advantage and the first-letter advantage were present throughout the entire range of exposure durations, whereas the central-letter advantage increased with longer exposures. On the other hand, increased spacing reduced both the outer-letter advantage and the first-letter advantage, whereas it led to a greater central-letter advantage. Changes in acuity and crowding as a function of stimulus exposure and inter-letter spacing, can account for this pattern of results.     

Brightness and loudness as functions of stimulus duration

The brightness of white light and the loudness of white noise were measured by magnitude estimation for sets of stimuli that varied in intensity and duration. Brightness and loudness both grow as power functions of duration up to a critical duration, beyond which apparent magnitude is essentially independent of duration. For brightness, the critical duration decreases with increasing intensity, but for loudness the critical duration is nearly constant at about 150 msec. Loudness and brightness also grow as power functions of intensity. The loudness exponent is the same for all durations, but the brightness exponent is about half again as large for short durations as for long. The psychophysical power functions were used to generate equal-loudness and equal-brightness functions, which specify the combinations of intensity E and duration T that produce the same apparent magnitude. Below the critical duration ET equals k for equal brightness, and ET^a equals k for equal loudness. The value a is about 0.7 for threshold and about 1.25 for supraliminal loudness.     

Response bias and the discrimination of stimulus duration

Pigeons discriminated stimulus duration in a psychophysical choice situation. Following presentation of any duration from a set of short duration (11 to 15 sec), responses on a red key were reinforced intermittently. Following presentation of any duration from a set of long durations (16 to 22 sec), responses on a green key were reinforced intermittently. Relative reinforcement rates were manipulated for choice responses across conditions. As relative reinforcement rates were varied, psychometric functions showed shifts in green-key responses at all durations. A signal-detection analysis showed that sensitivity remained roughly constant across conditions while response bias changed as a function of changes in relative reinforcement rate. Relative error rates tended to match relative reinforcement rates.     

Brightness and loudness as functions of stimulus duration

The brightness of white light and the loudness of white noise were measured by magnitude estimation for sets of stimuli that varied in intensity and duration. Brightness and loudness both grow as power functions of duration up to a critical duration, beyond which apparent magnitude is essentially independent of duration. For brightness, the critical duration decreases with increasing intensity, but for loudness the critical duration is nearly constant at about 150 msec. Loudness and brightness also grow as power functions of intensity. The loudness exponent is the same for all durations, but the brightness exponent is about half again as large for short durations as for long. The psychophysical power functions were used to generate equal-loudness and equal-brightness functions, which specify the combinations of intensity E and duration T that produce the same apparent magnitude. Below the critical duration ET equals k for equal brightness, and ET^a equa Is k for equal loudness. The value a is about 0.7 for threshold and about 1.25 for supraliminal loudness.     

Effect of stimulus pulse duration and interstimulus interval on cross-modal matching of auditory and lingual vibrotactile stimuli

Cross-modal matching functions for eight intensity levels of a 1000-Hz auditory stimulus and a 250-Hz lingual vibrotactile stimulus were obtained for two groups of subjects. Group 1 adjusted the vibrotactile stimulus to match the auditory stimulus, and Group 2 adjusted the auditory stimulus to match the vibrotactile stimulus. Stimulus-pulse durations and interstimulus intervals were varied over six experimental conditions for both groups. The variations in stimulus-pulse durations and interstimulus intervals had no appreciable effect on mean matching-function exponents for the two groups. A possible regression effect consistent with data from other psychophysical scaling studies was noted for matching functions of the two stimuli.     

Relative judgments affect assessments of stimulus duration

Humans were trained on two independent temporal discriminations, with correct choice dependent on the initial stimulus duration. In Experiment 1, the durations were 1.0 and 4.0 sec, with one set of choice stimuli, and 2.0 and 8.0 sec, with a different set of choice stimuli. The 2.0- and 4.0-sec values were selected to be the geometric mean of the two values in the other discrimination. In Experiment 2, the durations were 2.0 and 5.0 sec for one discrimination and 3.5 and 6.5 sec for the other. The 3.5- and 5.0-sec values were selected to be the arithmetic mean of the two values in the other discrimination. In both experiments, participants showed evidence for relational coding of the duration pairs. That is, the test durations were selected to be at the presumed bisection point (i.e., they should have produced indifferent choice), but instead the shorter test duration from the longer duration pair produced a “short” bias (in both experiments), whereas the longer duration from the shorter duration pair produced a “long” bias (in the second experiment). Results were similar to those from Zentall, Weaver, and Clement (2004) with pigeons.     

On the discriminability of stimulus duration.

The performance of pigeons trained to detect differences in the duration of stimuli was analysed using a matching model of signal detection. Two white stimuli, S1 and S2, differing in duration, were arranged with equal probability on the center key of a three-key chamber. S1 was systematically varied from 5 seconds to 25 seconds while S2 remained constant at 30 seconds. On completion of the center-key stimulus, a peck on the center key turned on the two red side keys. A left-key response was "correct" when S1 had been in effect on the center key and a right-key response was "correct" on S2 trials. A correct response produced a 3-second magazine light accompanied intermittently by food. Incorrect responses produced 3-second blackouts. Detection performance was measured under two procedures. In the first, the obtained reinforcement ratio was uncontrolled by allowing the number of food reinforcements obtained for correct left- and right-key responses to vary as the stimuli were changed. In the second procedure, the presentation of food reinforcement was controlled by holding the obtained reinforcement ratio constant. Discriminability changed as a function of stimulus differences under both procedures. No such trend was found in response bias.     

Vibrotactile thresholds during background vibration of long duration

Thresholds for vibrotactile stimuli of low and high frequency (20 and 150 Hz) were determined during a long-lasting (15 min) background stimulus of low or high frequency (40 or 240 Hz). Thresholds for high frequency were markedly elevated during both low and high frequency background stimulation, whereas thresholds for low frequency were elevated only at the beginning of high-frequency background stimulation. The present results indicate that during activation of the high-frequency vibrotactile channel it is possible to find both a cross-channel and a channel specific inhibition depending on the temporal parameters of the background stimulus. The effects of the present low-frequency background stimulus can be explained on the basis of a minor co-activation of the high-frequency channel.     

The effect of stimulus duration on the persistence of gratings

The persistence of gratings varying in spatial frequency and exposure duration was measured using a stimulus-blank alternation method. Persistence was found to lengthen with increasing spatial frequency and to shorten with increasing exposure duration. For each spatial frequency, persistence decreased linearly with a slope of approximately —.75 as duration increased for short stimulus durations. For longer stimulus durations, the rate of decline in persistence with increasing duration was reduced, the slope being approximately —.13. The stimulus duration at which the change in slope of the persistence-duration relationship occurred was shown to increase with increasing spatial frequency and was approximately equivalent to the critical duration for each spatial frequency. The data were consistent with an interpretation of persistence in terms of a temporal integration component and a second, possibly cortically located, component.     

Voice attractiveness: Influence of stimulus duration and type

Voice attractiveness is a relatively new area of research. Some aspects of the methodology used in this domain deserve particular attention. Especially, the duration of voice samples is often neglected as a factor and happens to be manipulated without the perceptual consequences of these manipulations being known. Moreover, the type of voice stimulus varies from a single vowel to complex sentences. The aim of this experiment was to investigate the extent to which stimulus duration (nonmanipulated vs. normalized) and type (vowel vs. word) influence perceived voice attractiveness. Twenty-seven male and female raters made attractiveness judgments of 30 male and female voice samples. Voice samples included a single vowel /a/, a three-vowel series /i a o/, and the French word “bonjour” (i.e., “hello”). These samples were presented in three conditions: nonmanipulated, shortened, and lengthened duration. Duration manipulation was performed using the pitch synchronous overlap and add (PSOLA) algorithm implemented in Praat. Results for the effect of stimulus type showed that word length samples were more attractive to the opposite sex than vowels. Results for the effect of duration showed that the nonmanipulated sound sample duration was not predictive of perceived attractiveness. Duration manipulation, on the other hand, altered perceived attractiveness for the lengthening condition. In particular, there was a linear decrease in attractiveness as a function of modification percentage (especially for the word, as compared with the vowels). Recommendations for voice sample normalization with the PSOLA algorithm are thus to prefer shortening over lengthening and, if not possible, to limit the extent of duration manipulation—for example, by normalizing to the mean sample duration.     

Effects of stimulus duration and choice delay on visual categorization in pigeons

We [Lazareva, O. F., Freiburger, K. L., & Wasserman, E. A. (2004). Pigeons concurrently categorize photographs at both basic and superordinate levels. Psychonomic Bulletin and Review, 11, 1111-1117] previously trained four pigeons to classify color photographs into their basic-level categories (cars, chairs, flowers, or people) or into their superordinate-level categories (natural or artificial). Here, we found that brief stimulus durations had the most detrimental effect on the basic-level discrimination of natural stimuli by the same pigeons. Increasing the delay between stimulus presentation and choice responding had greater detrimental effect on the basic-level discrimination than the superordinate-level discrimination. These results suggest that basic-level discriminations required longer stimulus durations and were more subject to forgetting than were superordinate-level discriminations. Additionally, categorization of natural stimuli required longer stimulus durations than categorization of artificial stimuli, but only at the basic level. Together, these findings suggest that basic-level categorization may not always be superior to superordinate-level categorization and provide additional evidence of a dissociation between natural and artificial stimuli in pigeons’ categorization.     

Effects of stimulus familiarity upon judged visual duration

Five experiments investigated the influence of the differences in stimulus familiarity among a dot-matrix letter, word, and nonword upon the relative judged duration of 30-msec flashes. Figure-ground contrast was manipulated by varying the number of dots comprising each display letter. With 30-msec presentations, judgments ranked subjective durations of the displays nonword > word > letter. Differences in judged duration among stimulus forms were greater when both forward and backward masking reduced recognition probability to chance level than when no mask was employed, and discriminations among masked presentations were easier for subjects. Figure-ground contrast influenced apparent duration judgments only as increases in figure-ground contrast contributed to clarity of familiarity differences among displays. The data were interpreted to indicate that differences in stimulus familiarity operate as early in visual processing as do differences in figure-ground contrast, with greater familiarity facilitating an automatic contact between a stimulus and its memory representation and therein reducing experienced duration.