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.     

Signal detectability in the presence of monotic or dichotic noise bands of equal or unequal levels

The application of the power-spectrum model of masking to the detectability of a signal masked by dichotic noise was investigated in three experiments. In each experiment, the signal was a 2-kHz sinusoid of 400-msec duration, masked by either one or two 800-Hz wide bands of noise presented singly or in pairs. In Experiment 1, we compared the detectability of a diotic signal masked by dichotic noise with the detectability of a monaural signal masked by each of the noises separately. The spectrum level of the noise was 35 dB SPL. For dichotic presentations, the signal was sent to both ears while pairs of noise bands, one below and one above the signal frequency, were presented together, one band to each ear. Threshold levels with the dichotic stimuli were lower than or equal to the thresholds with either ear's stimulus on its own. Similar dichotic stimuli were used in Experiment 2, except that the signal frequency was nearer to one or the other of the bands of masking noise, and the noise had a spectrum level of 50 dB SPL. In Experiment 3, thresholds were obtained with two sets of symmetrically and asymmetrically placed notched-noise maskers. For one of these sets, the spectrum level of both noise bands was 35 dB SPL; for the other set, interaural intensity differences were introduced in the form of an inequality in the levels of the noise bands on either side of the signal. In one ear, the spectrum level of the lower frequency noise band was 35 dB SPL and the spectrum level of the higher frequency noise band was 25 dB SPL, whereas in the other ear, the allocation of noise level to noise band was reversed. The dichotic thresholds obtained with the unequal noise maskers could be predicted from the shapes of the auditory filters derived with equal noise maskers. The data from all three experiments suggest that threshold signal levels in the presence of interaural differences in masker intensity depend principally on the ear with the higher signal-to-masker ratio at the output of its auditory filter, a finding consistent with the power-spectrum model of masking.     

On energy-dependent cues in duration discrimination

We consider the possibility that, in a duration discrimination task involving very short empty time intervals, T and T + ?T, bounded by brief auditory pulses, there may be a critical value of the base duration T within the range 50–300 msec below which duration is coded on the basis of sensory interactions between the markers which bound the interval. With ?T fixed at 10 msec, the functional relation between performance and base duration was determined under three levels of marker intensity. Changing the intensity by 37 dB resulted in the same small change in performance at the shortest base duration (50 msec), where it is most likely that an intensity-dependent interaction could be present, as was obtained at the longest base duration (250 msec), where such an interaction should be minimally effective as a cue for duration discrimination. The code for the duration of an empty auditory interval greater than 50 msee probably is not dorived from energy-dependent processes.     

Infants’ detection of increments in low- and high-frequency noise

A visually reinforced operant paradigm was employed to examine the relationship between the difference limen (DL) for intensity and level of the standard during infancy. In Experiment 1,7-month-old infants and adults detected increments in continuous noise presented via headphones at each of four levels ranging from 28 to 58 dB SPL. Noise stimuli were 2-octave bands centered at either 400 or 4000 Hz, and increments were 10 and 100 msec in duration. Infants’ DLs were significantly larger than those of adult subjects and significantly larger for low- than for high-frequency stimuli. For the high-frequency noise band, infants’ DLs were generally consistent with Weber’s law,remaining essentially constant for standards higher than 28 dB SPL (3 dB SL) for 100-msec increments and 38 dB SPL (13 dB SL) for 10-msec increments. For low-frequency noise, infants’ absolute thresholds were exceptionally high, and sensation levels of the standards were too low to adequately describe the relationship. In Ex-periment 2, 7-month-old infants detected 10- and 100-msec increments in 400-Hz noise stimuli presented in sound field. Infants’ low-frequency DLs were large at low intensities and decreased with increases in level of the standard up to at least 30 dB SL. For both low- and high-frequency noise, the difference between DLs for 10- and 100-msec increments tended to be large at low levels of the standard and to decrease at higher levels. These results suggest that the relationship between the DL and level of the standard varies with both stimulus frequency and duration during infancy. However, stimulus-dependent immaturities in increment detection may be most evident at levels within approximately 30 dB of absolute threshold.     

Effect of masker level on infants' detection of tones in noise

In adult listeners, the signal-to-noise ratio at masked threshold remains constant with increases in masker level over a wide range of stimulus conditions. This relationship was examined in 7-month-old infants by obtaining masked thresholds for .5- and 4-kHz tones presented in four levels of continuous masking noise. Adults were also tested for comparison. Masker spectrum levels ranged from 5 to 35 dB/Hz for .5-kHz tones, and from -5 to 25 dB/Hz for 4-kHz stimuli. Thresholds were determined for stimuli of both 10 and 100 msec in duration. The results indicated that infants' performance was more adult-like for 4-kHz stimuli. Although mean thresholds for both 10- and 100-msec, 4-kHz tones were approximately 7 dB higher in infants than in adults, E/N0 at threshold remained essentially constant over the 30-dB range of maskers employed. By contrast, infants' thresholds for .5-kHz tones were exceptionally high at lower levels of the masker. Threshold E/N0 decreased significantly as masker level increased from 5 to 35 dB/Hz, and this decrease was significantly greater for 10- than for 100-msec stimuli. Temporal summation of .5-kHz tones, measured as the difference between thresholds obtained at the two signal durations, was greater for infants than for adults at low levels of the masker. However, because infants' thresholds improved more rapidly with level for 10- than for 100-msec tones, age differences in temporal summation were no longer significant when masker spectrum level was 35 dB/Hz. These results suggest that the relationship between signal-to-noise ratio at masked threshold and level of the masker is dependent on both signal frequency and duration during infancy.     

Effect of masker level on infants’ detection of tones in noise

In adult listeners, the signal-to-noise ratio at masked threshold remains constant with increases in masker level over a wide range of stimulus conditions. This relationship was examined in 7-month-old infants by obtaining masked thresholds for .5- and 4-kHz tones presented in four levels of continuous masking noise. Adults were also tested for comparison. Masker spectrum levels ranged from 5 to 35 dB/Hz for .5-kHz tones, and from ?5 to 25 dB/Hz for 4-kHz stimuli. Thresholds were determined for stimuli of both 10 and 100 msec in duration. The results indicated that infants’ performance was more adultlike for 4-kHz stimuli. Although mean thresholds for both 10- and 100-msec, 4-kHz tones were approximately 7 dB higher in infants than in adults, E/N₀ at threshold remained essentially constant over the 30-dB range of maskers employed. By contrast, infants’ thresholds for .5-kHz tones were exceptionally high at lower levels of the masker. Threshold E/N0 decreased significantly as masker level increased from 5 to 35 dB/Hz, and this decrease was significantly greater for 10- than for 100-msec stimuli. Temporal summation of .5-kHz tones, measured as the difference between thresholds obtained at the two signal durations, was greater for infants than for adults at low levels of the masker. However, because infants’ thresholds improved more rapidly with level for 10- than for 100-msec tones, age differences in temporal summation were no longer significant when masker spectrum level was 35 dB/Hz. These results suggest that the relationship between signal-to-noise ratio at masked threshold and level of the masker is dependent on both signal frequency and duration during infancy.     

The effect of marker variability on the discrimination of temporal intervals

This research investigates the human observer’s ability to discriminate between the durations of two silent intervals, each interval preceded and followed by noise bursts called markers. The markers are separated by T or T + ΔT′ msec and T ranges from 0.3 to 1,000 msec. ΔT is defined as that value of ΔT′ for which the probability of discriminating T from T + ΔT′ is 0.75. We compared the value of AT for conditions in which the markers were fixed in amplitude and duration with conditions in which the marker amplitudes and durations were randomly chosen. ΔT increased by as much as a factor of 4 when the amplitude and duration of the markers were randomized. The performance decrement was primarily due to randomizing the first marker duration.     

Temporal discrimination as a function of marker duration

In a series of three experiments, the effect of marker duration on temporal discrimination was evaluated with empty auditory intervals bounded by markers ranging from 3 to 300 msec or presented as a gap within a continuous tone. As a measure of performance, difference thresholds in relation to a base duration of 50 msec were computed. Performance on temporal discrimination was significantly better with markers ranging from 3 to 150 msec than with markers ranging from 225 to 300 msec or under the gap condition. However, within each range of marker duration (3–150 msec; 225–300 msec or gap) performance did not differ significantly. A fourth experiment provided evidence that the effect of marker duration cannot be explained in terms of marker-induced masking. A good approximation of the relationship between marker duration and temporal discrimination performance in the present experiments is a smooth step function, which can account for 99.3% of the variance of mean discrimination performance. Thus, the findings of the present study point to the conclusion that two different mechanisms are used in the processing of temporal information, depending on the duration of the auditory markers. The tradeoff point for the hypothetical shift from one timing mechanism to the other may be found at a marker duration of approximately 200 msec.     

Control of responding by the location of an auditory stimulus: role of rise time of the stimulus

The control of responding by the location of tone bursts of 0.2- or 50-msec rise time was investigated in three albino rats. The apparatus consisted of an enclosure with two levers, two loudspeakers (in different locations), and a dipper feeder. The animal was exposed to tone bursts from either one or the other of the two speakers, and the speaker through which the tone bursts were delivered on any particular trial alternated in an irregular manner. Responses on one lever were reinforced with food in the presence of tone bursts from one speaker; responses on the second lever were reinforced with food in the presence of tone bursts from the second speaker. Responding came under the control of the location of 4-kHz tone bursts of 0.2-msec rise time within the first session. At this rise time, animals maintained a stable level of correct responding of greater than 95%. When the rise time was increased to 50 msec the percentage of correct responding fell to an average of 80 to 85%. It was concluded that location of an auditory stimulus is a powerful controller of responding in rats and that the degree of control is dependent upon rise time.     

Auditory evoked brain responses: Comparison of ON and OFF responses at long and short durations

Average evoked brain responses (EBRs) to three durations of one kilohertz pure-tone stimuli were computed from human scalp recordings. Stimuli of 25, 75, and 2,000 msec duration were each presented binaurally at each of eight equally spaced intensity levels, ranging from 58 to 86 dB SPL. EBRs computed immediately following presentation, and immediately following removal of the 2,000-msec-duration stimulus result in ON and OFF responses, respectively. EBRs computed immediately following presentation of the 25- and 75-msec-duration stimuli appear to be the result of the sum of separate responses to stimulus onset and offset. Computer-dissected ON and OFF EBRs to short-duration stimuli are very similar in waveform and amplitude to the responses evoked by the onset and offset, respectively, of the 2,000-msec duration stimulus. Dissected ON and OFF responses demonstrate linear amplitude-intensity functions in amplitude ranges similar to respective ON and OFF responses to 2,000-msec stimulation. The data suggest that ON and OFF responses are mediated by independent physiological mechanisms.     

Enhancement,extension, and reversal of the frequency selectivity effect

The influence of a frequency cue on judgments of whether or not a subsequent target incorporated a brief silent gap was examined. In Experiment 1, there was no predictive frequency relation and evidence of auditory inhibition of return was obtained with frequency repetitions, producing a facilitative effect at 175-msec stimulus onset asynchrony (SOA) and an inhibitory effect at 775-msec SOA. Relative to this baseline performance pattern, increasing the probability of a frequency match to .75 (Experiment 2) served to generate a beneficial effect of frequency repetitions at lengthy SOAs and to enlarge its magnitude at 175-msec SOA. In contrast, a reduction in the probability of a frequency match to .25 (Experiment 3) resulted in the elimination of any facilitative effect of repetition at 175-msec SOA and the development of an inhibitory effect at 475- and 1,075-msec SOA. These results establish that a frequency cue may engage both exogenous and endogenous attentional processes within 175 msec following its presentation.     

The influence of cognitive set on performance and arousal under different noise loads

Three groups of 12 subjects each performed a mental arithmetic task while exposed to continuous white noise in two experimental sessions. In Session I, each group was exposed to a different noise level [56, 72.5, or 85dB(A)], whereas in Session II all had the medium [72.5 dB(A)] intensity. Arithmetic performance deteriorated with increasing noise intensity in Session I, and in Session II each group retained its position relative to the other two groups. Thus, the higher the noise intensity in the first session, the poorer the performance in the second session. These results suggest that the motivation and energy mobilized in Session II were determined by the cognitive set adopted to meet the demands of Session I. Arousal level, as measured by adrenaline excretion and heart rate, was higher during both experimental sessions than in a control session. The rise in adrenaline output was of the same magnitude regardless of the intensity of the noise, which indicates that the subjects adjusted to the increase in total load by slowing down their performance rather than by raising their energy mobilization. Heart rate rose in response to changes in noise level in Session II relative to Session I, regardless of the direction of the change.     

Facilitative and inhibitory effects of cuing sound duration, intensity, and timbre.

Two experiments are reported in which the possibility that auditory attention may be controlled in a stimulus-driven manner by duration, intensity, and timbre cues was examined. In both experiments, listeners were presented with a cue followed, after a variable time period of a 150-, 450-, or 750-msec stimulus onset asynchrony (SOA), by a target. In three different conditions for each experiment, the duration, intensity, or timbre relation between the cue and the target was varied so that, on 50% of the trials, the two sounds were identical and, on 50% of the trials, the two sounds were different in the manipulated feature. The two experiments differed only in the judgment required, with listeners in Experiment 1 identifying the duration, intensity, or timbre of the target and listeners in Experiment 2 indicating whether the target incorporated a brief silent gap. In both experiments, performance was observed to depend on both the similarity of and the time between the cue and the target. Specifically, whereas at the 150-msec SOA performance was best when the target was identical to the preceding cue, at the 750-msec SOA performance was best when the cue and the target differed. This pattern establishes the existence of duration-, intensity-, and timbre-based auditory inhibition of return. The theoretical implications of these results are considered.     

Facilitative and inhibitory effects of cuing sound duration, intensity, and timbre

Two experiments are reported in which the possibility that auditory attention may be controlled in a stimulus-driven manner by duration, intensity, and timbre cues was examined. In both experiments, listeners were presented with a cue followed, after a variable time period of a 150-, 450-, or 750-msec stimulus onset asynchrony (SOA), by a target. In three different conditions for each experiment, the duration, intensity, or timbre relation between the cue and the target was varied so that, on 50% of the trials, the two sounds were identical and, on 50% of the trials, the two sounds were different in the manipulated feature. The two experiments differed only in the judgment required, with listeners in Experiment 1 identifying the duration, intensity, or timbre of the target and listeners in Experiment 2 indicating whether the target incorporated a brief silent gap. In both experiments, performance was observed to depend on both the similarity of and the time between the cue and the target. Specifically, whereas at the 150-msec SOA performance was best when the target was identical to the preceding cue, at the 750-msec SOA performance was best when the cue and the target differed. This pattern establishes the existence of duration-, intensity-, and timbre-based auditory inhibition of return. The theoretical implications of these results are considered.     

Effects of practice and signal energy on duration discrimination of brief auditory intervals

In Experiment 1, the proposition that duration discrimination of filled auditory intervals is based on temporal information rather than on energy-dependent cues was tested in 64 naive subjects. The subjects were presented with two auditory stimuli at different levels of intensity within one trial, and had to decide which of the two was longer in duration. An adaptive psychophysical procedure was used. As a measure of performance, difference threshold estimates in relation to a 50-msec standard interval were computed. Duration discrimination showed no effect of energy values, indicating that the subjects’ discrimination was independent of stimulus intensity. The goal of Experiments 2A and 2B was to investigate the effects of practice on duration discrimination which, in addition, may provide an indirect test for the potential use of energy-dependent cues. Effects of practice on duration discrimination of filled (Experiment 2 A) and empty (Experiment 2B) intervals were studied in 6 subjects in each case, over 20 testing sessions. An adaptive psychophysical procedure that was similar to the one used in Experiment 1 was applied. Neither short-term effects of practice based on the first five testing sessions, nor long-term effects of practice based on the means of 4 consecutive weeks, could be demonstrated. The results of the present study suggest that duration discrimination of brief auditory intervals is based on temporal information and not on stimulus energy. Furthermore, implications for the notion of a very basic bio-logical timing mechanism underlying temporal processing of brief auditory intervals in the range of milliseconds are discussed.     

Auditory temporal summation in infants and adults: Effects of stimulus bandwidth and masking noise

A visually reinforced operant procedure was employed to determine the behavioral thresholds of 6- to 7-month-old infants and adults for stimuli of various bandwidths and durations. Experiment 1 compared absolute thresholds for broadband and 1/3-octavefiltered clicks and 300-msec noise bursts. For adult subjects, the difference in threshold for clicks and noise bursts was -quite comparable in the two bandwidth conditions, but infants’ click-noise threshold differences were significantly larger for broadband than for 1/3-octave stimuli. In Experiment 2, 2-point threshold-duration functions were compared for 4-kHz tones and octave-band noise bursts presented in backgrounds of quiet and continuous noise. Infants’ threshold-duration function for octave-band noise bursts was significantly steeper than the comparable adult function in quiet, but not in masking noise. These results suggest that young infants may have particular difficulty detecting low intensity broadband sounds when durations are very short.     

The effects of marker-related temporal cues on auditory gap-duration discrimination

In three experiments, we examined the ability of listeners to discriminate the duration of temporal gaps (silent intervals) and the influence of other temporal stimulus properties on their performance. In the first experiment, gap-duration discrimination thresholds were measured either in continuous noise or with noise markers with durations of 3 and 300 ms. Thresholds measured with 300-ms markers differed from those measured in continuous noise or with 3-ms markers. In the second experiment, stimuli consisting of a gap between two discrete markers were generated such that the gap duration, the onset-to-onset duration between markers, and the duration of the first marker were pseudorandomized across trials. Listeners’ responses generally were consistent with the cue that was identified as the target cue from among the three cues in each block of trials, but the data suggested that the onset-to-onset cue was particularly salient in all conditions. Using a modified method-of-adjustment procedure in the third experiment, subjects were instructed to discriminate between the durations of gaps in discrete markers of different durations in two intervals, where the gap duration in one interval was adapted to measure the point of subjective equality. Without feedback, listeners tended to equate the onset-to-onset times of the markers rather than the gap durations. Overall, the results indicated that listeners’ judgments of silent gaps between two discrete markers are strongly influenced by the onset-to-onset time, or rhythm, of the markers.     

The effects of type of interval,sensory modality,base duration,and psychophysical task on the discrimination of brief time intervals

The present study was designed to investigate the influences of type of psychophysical task (two-alternative forced-choice [2AFC] and reminder tasks), type of interval (filled vs. empty), sensory modality (auditory vs. visual), and base duration (ranging from 100 through 1,000 ms) on performance on duration discrimination. All of these factors were systematically varied in an experiment comprising 192 participants. This approach allowed for obtaining information not only on the general (main) effect of each factor alone, but also on the functional interplay and mutual interactions of some or all of these factors combined. Temporal sensitivity was markedly higher for auditory than for visual intervals, as well as for the reminder relative to the 2AFC task. With regard to base duration, discrimination performance deteriorated with decreasing base durations for intervals below 400 ms, whereas longer intervals were not affected. No indication emerged that overall performance on duration discrimination was influenced by the type of interval, and only two significant interactions were apparent: Base Duration × Type of Interval and Base Duration × Sensory Modality. With filled intervals, the deteriorating effect of base duration was limited to very brief base durations, not exceeding 100 ms, whereas with empty intervals, temporal discriminability was also affected for the 200-ms base duration. Similarly, the performance decrement observed with visual relative to auditory intervals increased with decreasing base durations. These findings suggest that type of task, sensory modality, and base duration represent largely independent sources of variance for performance on duration discrimination that can be accounted for by distinct nontemporal mechanisms.     

The effects of lead stimulus and reflex stimulus modality on modulation of the blink reflex at very short, short, and long lead intervals

The blink reflex is modulated if a weak lead stimulus precedes the blink-eliciting stimulus. In two experiments, we examined the effects of the sensory modality of the lead and blink-eliciting stimuli on blink modulation. Acoustic, visual, or tactile lead stimuli were followed by an acoustic (Experiment 1) or an electrotactile (Experiment 2) blink-eliciting stimulus at lead intervals of -30, 0, 30, 60, 120, 240, 360, and 4,500 msec. The inhibition of blink magnitude at the short (60- to 360-msec) lead intervals and the facilitation of blink magnitude at the long (4,500-msec) lead interval observed for each lead stimulus modality was relatively unaffected by the blink-eliciting stimulus modality. The facilitation of blink magnitude at the very short (-30- to 30-msec) lead intervals was dependent on the combination of the lead and the blink-eliciting stimulus modalities. Modality specific and nonspecific processes operate at different levels of perceptual processing.     

Identification of microtonal melodies: Effects of scale-step size,serial order,and training

The perception of microtonal scales was investigated in a melodic identification task. In each trial, eight pure tones, equally-spaced in log frequency in the vicinity of 700 Hz, were presented in one of nine different serial orders. There were two experiments, each with 108 trials (six scales [tone sets] × nine serial orders × two repetitions). In each experiment, 30 subjects, half of whom were musically trained, were asked to match each melody to one of 9 visual representations (frequency-time grids). In Experiment 1, the six scales were spaced at intervals of 25, 33, 50, 67, 100, and 133 cents (100 cents=1 semitone ≈6% of frequency). Performance was worse for scale steps of 25 and 33 cents than it was for wider scale steps. There were no significant effects at other intervals, including the interval of 100 cents, implying that melodic pattern identification is unaffected by long-term experience of music in 12-tone equally tempered tuning (e.g., piano music). In Experiment 2, the six scales were spaced at smaller intervals, of 10, 20, 30, 40, 50, and 60 cents. Performance for the three narrower scale steps was worse than that for the three wider scale steps. For some orders, performance for the narrowest scale step (10 cents) did not exceed chance. The smallest practical scale step for short microtonal melodies in a pattern-identification task was estimated as being 10–20 cents for chance performance, and 30–40 cents for asymptotic performance.