The subjective tempo difference between interaural and monaural sequences as a function of sequence length

Previous research has demonstrated that the subjective tempo of sequences of clicks that alternate between ears is slower than that of nonalternating sequences. Although the stimulus onset asynchronies (SOAs) between the clicks are the same in both conditions, their perceptual onset asynchronies (POAs) differ by 25 msec at all SOA values between 40 and 2,130 msec. It has been suggested that this subjective tempo difference originates only after a few clicks have been processed. The present study shows this not to be the case: The POA difference between interaural and monaural click sequences could also be established with sequences comprising only a few clicks.     

Discrimination of auditory temporal patterns

Two same-different discrimination experiments were performed for click patterns having a total duration of about 4 sec and interclick intervals ofn × 250 msec, withn a random integer. In Experiment 1, the influence of the physical click group structure on discrimination performance was investigated. In Experiment 2, the effect of the strength of an induced internal clock on discrimination performance was measured. Performance was poor if the group structure of clicks was maintained during a change in click pattern and also if the induced infernal clack strength was low. The performance of about 70% of the subjects improved significantly if either a change in click grouping structure occurred or a strong internal clock could be induced. These results cannot be accounted for with simple models based an single-interval duration discrimination or between-pattern correlation statistics.     

Effect of click rate and delay on breakdown of the precedence effect

The precedence effect was tested as a function of echo-click delay and click rate after an abrupt switch in location between leading and lagging clicks. Click trains at three rates, 1/sec, 2/sec, and 4/sec, with delays ranging between 2 and 20 msec, were presented to subjects in an anechoic chamber. Duration of the click train after the switch in location was 12 sec, and echo click perceptibility was assessed throughout this period. The number of echo clicks heard was an increasing monotonic function of delay. The subjects reported a "fade-out" of echo clicks after a set number of clicks at each delay, regardless of rate. This result was interpreted as a buildup in inhibition of echoes produced by the ongoing click train. Suppression of echoes was stronger when the leading click originated from the right side than from the left side.     

Spatial stimulus cue information supplying auditory saltation

Auditory saltation is a misperception of the spatial location of repetitive, transient stimuli. It arises when clicks at one location are followed in perfect temporal cadence by identical clicks at a second location. This report describes two psychophysical experiments designed to examine the sensitivity of auditory saltation to different stimulus cues for auditory spatial perception. Experiment 1 was a dichotic study in which six different six-click train stimuli were used to generate the saltation effect. Clicks lateralised by using interaural time differences and clicks lateralised by using interaural level differences produced equivalent saltation effects, confirming an earlier finding. Switching the stimulus cue from an interaural time difference to an interaural level difference (or the reverse) in mid train was inconsequential to the saltation illusion. Experiment 2 was a free-field study in which subjects rated the illusory motion generated by clicks emitted from two sound sources symmetrically disposed around the interaural axis, ie on the same cone of confusion in the auditory hemifield opposite one ear. Stimuli in such positions produce spatial location judgments that are based more heavily on monaural spectral information than on binaural computations. The free-field stimuli produced robust saltation. The data from both experiments are consistent with the view that auditory saltation can emerge from spatial processing, irrespective of the stimulus cue information used to determine click laterality or location.     

The effect of masker duration on forward and backward masking

Temporal masking of clicks by noise was investigated using forward and backward masking paradigms. Both the noise duration and the temporal separation, ΔT, between the click and noise were varied. For very brief ΔTs (100 microsec) and for very long ΔTs (100 msec), the duration of the masker did not greatly affect the click threshold. However, for intermediate ΔTs (3 msec), the threshold increased by as much as 44 dB as the noise duration increased from 0.1 to 100 msec. Temporal weighting functions, which describe the relative effectiveness of the noise as a function of ΔT, were computed from these data.     

Auditory saltation in the vertical midsagittal plane

Auditory saltation is an illusion in which a train of clicks, the first half of which is presented at one location and the other half of which is presented from a second location, is perceived as originating not only from the anchor points, but also from locations between them. That is, intermediate members of the series of clicks have their spatial locations systematically misperceived. In the present study, auditory saltation was examined for the first time in the vertical midsagittal plane. Subjects rated the perceived continuity of motion for 8-click trains systematically varied in inter-click interval (ICI), direction of motion (up, down), and trial type ('saltation' versus 'real' motion). In all listeners, saltation stimuli supported robust saltation, but only for trials with ICIs less than about 120 ms. Real motion was rated as continuous for all ICIs. These data indicate that the auditory-saltation illusion can exploit monaural stimulus cues for source location in the generation of the illusory motion percept.     

Interaural and monaural clicks and clocks: tempo difference versus attention switching

We describe a quantitative model capable of explaining the results of all reported investigations of the counting of interaural and monaural click sequencies. The model is developed by means of three convergent operations: (a) reanalyzing absolute-estimation data of apparent repetition rates of interaural and monaural sequences, (b) deriving interaural and monaural counting times from numerosity-judgement data, and (c) analyzing the time that observers needed to respond to the end of interaural and monaural sequences. The combined evidence demonstrates that the perceived onset asynchrony (POA) between interaural events is 24 msec longer than that between monaural events. The model has three components: (a) a "stimulus clock," which represents the stimulus onset synchrony (SOA) between events; (b) a "memory clock," which represents the POA between events, and (c) a "counting clock," which represents the counter increment time. The transfer functions between the three clocks are deduced from empirical data. Other proposals to explain interaural click counting results (attention switching, streaming by locus, counterincrement deficit) are discussed and rejected.     

Attention-switching and grouping in counting interaurally presented clicks.

The present study tests the hypothesis that attention-switching is time-consuming and performance-limiting. Analysis of previous research on counting interaurally presented clicks shows that estimates of ‘switch-times’ can be made, based on the data of Guzy and Axelrod (1972). In the earlier click-counting studies, however, the number of clicks to be counted and the number of physical switches between the ears were confouned. Hence the number of clicks, number of physical switches and interval between clicks were independently varied. The results showed that (a) counting performance did not decrease monotonically with increasing number of switches in the click sequence; (b) no difference in counting performance could be found between the monaural and completely alternating interaural presentation; (c) when the number of switches in the sequence was small and equal groups of clicks alternated between ears, performance dramatically improved. With these kinds of sequences, subjects presumably do not count the clicks one at a time, but subitize a group of clicks.     

Lateralization of two-transient stimuli

In this study of the precedence effect in binaural hearing, subjects adjusted the interaural delay of a wideband acoustic pointer to match the perceived intracranial position of transient test stimuli presented over headphones. The test stimuli had leading and lagging components (either brief noise bursts or clicks), each with its own interaural delay. In some test conditions, the leading and lagging stimuli were coherent copies of one another, whereas in others, they were independent samples of noise. The duration of the stimuli and the delay from the leading component to the lagging component were also varied. All the stimulus conditions showed a moderate or strong precedence effect (i.e., covariation of perceived lateral position of the composite two-transient stimulus with the interaural delay of the leading component). Predictions of the lateralization data are presented for variants of models based on temporal weighting and/or bandpass correlation. In one model variant, the binaural stimuli are temporally weighted to emphasize the onset and then subjected to bandpass correlation analysis. In another variant, it is assumed that the onset mechanism provides a rough estimate of the initial interaural delay that guides a slower and more focused bandpass correlation analysis. The accuracies of these two model's predictions were equivalent and superior to those of models that either represent leading and lagging cues equally (bandpass correlation with no onset effect) or do not represent lagging cues at all (a complete precedence effect). The results of these analyses show the need for both a strong onset effect and for bandpass correlation analysis and suggest two modeling approaches for achieving that goal.     

Synchronizing actions with events: The role of sensory information

Tasks requiring the subject to tap in synchrony to a regular sequence of stimulus events (e.g., clicks) usually elicit a response pattern in which the tap precedes the click by about 30-50 msec. This “negative asynchrony” was examined, first, by instructing subjects to use different effectors for tapping (hand vs. foot; Experiments 1 and 2), and second, by administering extrinsic auditory feedback in addition to the intrinsic tactile/kinesthetic feedback (Experiment 2). Experiment 3 controlled whether the results observed in Experiment 2 were due to purely sensory factors within the auditory modality. Results suggest that taps are synchronized with clicks at the central level by superimposing two sensory codes in time: the tactile/kinesthetic code that represents the tap (the afferent movement code) and the auditory code that represents the click (the afferent code that results from the guiding signal). Because the processing times involved in code generation are different for these two central codes, the tap has to lead over the click.     

The detection of anisochrony in monaural and interaural sound sequences

Nakao and Axelrod (1976) and van Noorden (1975) showed that the threshold for discriminating an anisochronous duple rhythm (a series of clicks with a temporal offset on every other one) from an isochronous rhythm (no offset) is poorer when the clicks are presented alternately to the two ears than when they are presented to the same ears. Van Noorden reported that the difference between the thresholds in the alternating and nonalternating conditions varied with the tempo of the sequence. Nakao and Axelrod found invariance of this threshold difference with sequence speed. According to our quantification of temporal processing of interaural sequences, the latter result should be expected. We carried out five psychophysical experiments to establish interaural and monaural discrimination between isochronous and anisochronous rhythms. Across experiments, base time intervals of 60–720 msec were spanned. The main result was that we replicated the poorer discrimination for interaural sequences. This deterioration in discrimination was the same for all sequence speeds. It was also the case that the thresholds were almost constant up to a sound repetition rate of about 3 per second, but increased linearly with slower rates. This result supports evidence in the literature that temporal processing of sequences faster than about 3–4 sounds per second differs from temporal processing of slower sequences.     

Antecedents of Leader Utilization of Staff Input in Decision-Making Teams

The purpose of this experiment was to explore the possibility that the inconsistent findings of Brehmer and Hagafors (1986,Organizational Behavior and Human Decision Processes, 38, 181–195), Sniezek and Buckley (1995,Organizational Behavior and Human Decision Processes, 62, 159–174), and leader–member exchange research regarding leaders' propensity todifferentiallyandaccuratelyweight staff input can be explained as a result of experience, the availability to the leader of staff member judgment confidence, and the cumulative past accuracy of each staff member. The availability to the team leader of staff member past judgment accuracy and staff member judgment confidence was provided in an environment in which differential staff weighting was the appropriate staff utilization strategy. Eighty-four leaders of four-person decision-making teams performed 63 decisions on a computerized decision-making task. Both experience and providing leaders with cumulative staff past accuracy information were related to greater staff weighting variability and greater staff weighting accuracy. Although positively related to staff weighting, staff confidence information did not improve leader weighting variability nor actual staff weighting accuracy.     

Differences in American English, Spanish, and monkey perception of thesay-stay trading relation

An interesting phenomenon in human speech perception is the trading relation, in which two different acoustic cues both signal the same phonetic percept. The present study compared American English, Spanish, and monkey listeners in their perception of the trading relation between gap duration andFl transition onset frequency in a syntheticsay-stay continuum. For all the subjects, increased gap duration caused perception to change fromsay tostay; however, subjects differed in the extent to which theFl cue traded with gap duration. For American English listeners, a change from a low to a highF1 onset caused a phoneme boundary shift of 26 msec toward shorter gap durations, indicating a strong trading relation. For Spanish listeners, the shift was significantly smaller at 13.7 msec, indicating a weaker trading relation. For monkeys, there was no shift at all, indicating no trading relation. These results provide evidence that thesay-stay trading relation is dependent on perceptual learning from linguistic exposure.     

Behavioral discrimination of click intensity in cat

Avoidance conditioning procedures were used to train cats to discriminate intensity differences between successive clicks. The discriminative behavior was applied in a modified method of adjustment to determine a difference limen (DL) for click intensity. The obtained DLs were consistent within and between subjects, and averaged 4.4 db. This value is greater than previously reported intensity DLs for pure tones in cats.     

Persistence and integration: Two consequences of a sliding integrator

The detection of a silent interval, or gap, placed in the temporal center of a gated noise burst was investigated. The gated noise masker ranged from 2 to 400 msec in duration. For long noises, the duration, Δ, of the just-detectable gap remained fixed at about 2.8 msec. Progressively shortening the duration of the noise did not affect Δ until the duration was approximately 20 msec; thereafter, decreasing the noise duration improved detectability of the gap. In a second experiment, continuous noise filled the temporal gap, although the decibel difference between the noise in the gap and the noise surrounding the gap was always at least 5 dB. The level of noise filling the gap did not greatly affect Δ. The third experiment was similar to the first, except that the signal was a click rather than a gap. The results for both gaps and clicks were fitted by a model assuming a sliding integrator.     

The relative weighting of acoustic properties in the perception of [s]+stop clusters by children and adults

We examined the perceptual weighting by children and adults of the acoustic properties specifying complete closure of the vocal tract following a syllable-initial [s]. Experiment 1 was a novel manipulation of previously examined acoustic properties (duration of a silent gap and first formant transition) and showed that children weight the first formant transition more than adults. Experiment 2, an acoustic analysis of naturally producedsay andstay, revealed that, contrary to expectations, a burst can be present instay and that first formant transitions do not necessarily distinguishsay andstay in natural tokens. Experiment 3 manipulated natural speech portions to create stimuli that varied primarily in the duration of the silent gap and in the presence or absence of a stop burst, and showed that children weight these stop bursts less than adults. Taken together, the perception experiments support claims that children integrate multiple acoustic properties as adults do, but that they weight dynamic properties of the signal more than adults and weight static properties less.     

Visual perseveration in normal and mentally retarded children

Visual perseveration was investigated within mentally retarded and second, fifth, and eighth grade normal children (Ns = 12 each group). Subjects matched an auditorially presented click to the onset and offset of visually presented stimuli. Time differences between visual stimulus offset and the point at which subjects reported simultaneity of the click and visual stimulus offset was assumed to reflect visual perseveration. Results showed: (a) no differences between the normal children as a function of age; (b) no difference between groups for stimuli of 100 msec. or longer duration; and (c) retarded subjects judged stimuli of 20 and 50 msec. to be of shorter duration than did normal subjects. This highly specific distinction between retarded and normal subjects suggests a difference in an early stage of perceptual processing.     

Judging the time to collision with a simulated textured object: Effect of mismatching rate of expansion of object size and of texture element size

We measured the accuracy with which subjects estimated the time to collision with a simulated textured object approaching at constant speed along the line of sight. The independent variable was the ratioR, whereR = (rate of dilation of the texture elements that covered the simulated object) / (rate of dilation of object size). When matching was perfect (i.e.,R = 1.0), the mean of 12 settings was close to the nominal value of 2,000 msec for both subjects. In addition, the standard error of 12 settings was only 25 and 52 msec in 2,000 msec for the 2 subjects. Discrimination threshold for time to collision was not significantly affected byR over the range investigated betweenR = 0 andR = 2.0. However, the accuracy of estimating time to collision was significantly affected byR. Estimated time to collision was a monotonic function ofR. For example, when the mismatch was only 10% (i.e.,R = 0.9) subjects judged time to collision would occur 178 msec later than the true time to collision of 2,000 msec.     

Temporal brightness enhancement: Studies of individual differences

We have previously identified categorical individual differences in the occurrence of temporal brightness enhancement (TBE) by using a simultaneous brightness discrimination paradigm (Bowen & Markell, 1980).TBE is a nonmonotonic relation between brightness and pulse duration, pulses of intermediate duration (75–125 msec) can appear brighter than longer or shorter pulses of the same luminance. Three classes of observers can be defined based on whether they perceive TBE under one of two conditions of temporal asynchrony between a short test pulse and a longer (500 msec) comparison pulse:simultaneous onset of the pulses orsimultaneous offset. Type A observers show TBE for both asynchrony conditions; Type B observers show the effect for simultaneous offset but not simultaneous onset; Type C observers do not show TBE for either asynchrony. In the present study, we show that Type A and Type C observers maintain a constant brightness-duration relation as the asynchrony between test and comparison pulses is varied from simultaneous onset to simultaneous offset. Type B observers show a gradual shift in the brightness-duration relation as asynchrony changes. In a separate experiment, we find that practice has little effect on Type A and Type B observers but that Type C observers may change in classification to Types A and B over as few as five experimental sessions. The hypothesis that individual differences are due to differential “weighting” of chromatic (sustained) and achromatic (transient) visual channels is discussed.