Comparing adaptive procedures for estimating the psychometric function for an auditory gap detection task

A subject’s sensitivity to a stimulus variation can be studied by estimating the psychometric function. Generally speaking, three parameters of the psychometric function are of interest: the performance threshold, the slope of the function, and the rate at which attention lapses occur. In the present study, three psychophysical procedures were used to estimate the three-parameter psychometric function for an auditory gap detection task. These were an up–down staircase (up–down) procedure, an entropy-based Bayesian (entropy) procedure, and an updated maximum-likelihood (UML) procedure. Data collected from four young, normal-hearing listeners showed that while all three procedures provided similar estimates of the threshold parameter, the up–down procedure performed slightly better in estimating the slope and lapse rate for 200 trials of data collection. When the lapse rate was increased by mixing in random responses for the three adaptive procedures, the larger lapse rate was especially detrimental to the efficiency of the up–down procedure, and the UML procedure provided better estimates of the threshold and slope than did the other two procedures.     

The relation between gap discrimination and auditory stream segregation

Gap discrimination and stream segregation were examined using sequences of 2, 4, 8, or 16 tones. The frequency differences between tones ranged from 1/24 to 2 1/2 octaves. Judgments of stream segregation show large intersubject variability, whereas gap thresholds are comparatively stable. Gap thresholds and streaming judgments are both affected by the frequency separation between tones. However, only streaming judgments are affected by presentation rate. Gap-threshold functions show no discontinuities or plateaus with increasing frequency differences and faster presentation rates. These results suggest that stream segregation is not a primary factor limiting gap-discrimination performance in tonal sequences.     

Tactile gap detection and language lateralization

Recent work suggests that hemispheric language lateralization might be related to the fine-grained temporal discriminations that are required for linguistic processing (Nicholls, 1996). Studies concerning tactile processing have also shown a significant left-hemisphere (L-H) advantage for tactile gap detection (Nicholls & Whelan, 1997). We hypothesized that language and tactile processing are both preferentially processed by the left hemisphere because it is specialized for tasks requiring fine-grained temporal resolution. Thirty-two participants (16 right and 16 left handers) were tested for both linguistic processing (using the Fused Dichotic Words Test (FDWT)) and tactile gap detection. Both right and left handers showed a significant L-H advantage for both language processing and tactile gap detection. The present study supports recent claims that language lateralization is attributable to the left hemisphere's better suitability to process tasks that require fine-grained temporal resolution.     

Interval of time uncertainty in visual detection

The effects of increasing the length of an interval of continuous temporal uncertainty (ITU) on the detectability of visualsignals were investigated in a ‘Yes/No’ detection situation. Ss were uncerlain about when a signal might occur within a given observalion interval, the duration of which was varied. Longer intervals of uncertainty resulted in a decrement in detectability, which was shown to be directly attributable to increased false alarm rates. It was suggested that observers have more opportunities for confusing signals with noise. The time course of detectability within a givenITU was also investigated, but there were no significant variations.     

Spatio-temporal effects in visual gap detection

The ability of the visual system to process temporal information is studied with regard to the interactions between temporal and spatial stimulus dimensions. A comparison of the results of two experiments indicate that the eye is able to discriminate temporal gaps in a train of visual flashes better when the flashes are spatially superposed then when they are dispersed. Thus, the inertial and integrating properties of the visual receptor seem, at first glance, to hinder the discrimination less than does spatial dispersion. However, an analysis of the results, using Levinson’s low-pass filter model, suggests that the increased discrimination is due to the recoding of the temporal stimulus information along a brightness dimension, and thus the true temporal properties of the visual system are probably better described by the dispersed rather than the overlapped condition. Other experiments are also reported that deal with related phenomena germane to the ability of human Ss to deal with the temporal information pattern of visual stimuli.     

Parameters affecting gap detection in the rat

The present research used a startle amplitude reduction paradigm to investigate the ability of the rat’s auditory system to track rapidly changing acoustic transients. Specifically examined was the ability of brief gaps in otherwise continuous noise to reduce the amplitude of a subsequently elicited acoustic startle reflex. The duration of the gap, time between gap offsetand startle elicitation (the interstimulus interval or ISI), and rise-fall characteristics of the gap were systematically varied. Consistent with previous research, gaps reliably reduced startle amplitude. Gaps 2 msec long were reliably detected, and a 50-msec ISI resulted in the greatest amplitude reduction. Gaps presented at short ISIs produced amplitude reduction that followed a different time course than did gaps presented at longer ISIs. These results may reflect differences in the length oftime available for the processing of the stimulus and may involve two different processes.     

Critical-band effects in two-channel auditory signal detection

Two-channel auditory signal detection was investigated with 50-msec sinusoidal signals masked by binaurally uncorrelated noise. In the two-channel tasks, the signals in each earphone channel were presented with an independent probability during the single observation interval and the observers were required to detect the inputs in a single earphone (selective-attention condition) or in both earphones (divided-attention condition). When the signals in each earphone were within the same critical band (the assumed singled processing unit in frequency domain), there was a decrement in detection performance in both the selective- and divided-attention (i.e. dichotic) conditions compared with the monaural condition. However, when signals were separated in frequency by several critical bands, a decrement in dichotic performance, as compared with monaural performance, occurred only in the divided-attention condition. These findings are discussed in terms of their implications regarding models of multichannel signal processing and the definition of input channels in terms of earphones.     

Interval timing with gaps: gap ambiguity as an alternative to temporal decay

C. V. Buhusi, D. Perera, and W. H. Meck (2005) proposed a hypothesis of timing in rats to account for the results of experiments that have used the peak procedure with gaps. According to this hypothesis, the introduction of a gap causes the animal's memory for the pregap interval to passively decay (subjectively shorten) in direct proportion to the duration and salience of the gap. Thus, animals should pause with short, nonsalient gaps but should reset their clock with longer, salient gaps. The present authors suggest that the ambiguity of the gap (i.e., the similarity between the gap and the intertrial interval in both appearance and relative duration) causes the animal to actively reset the clock and prevents adequate assessments of the fate of timed intervals prior to the gap. Furthermore, when the intertrial interval is discriminable from the gap, the evidence suggests that timed intervals prior to the gap are not lost but are retained in memory.     

Cueing signals in auditory detection and frequency discrimination experiments

The effects of presenting a cueing signal during the warning interval initiating a trial were investigated in two-interval forced-choice detection and frequency-discrimination experiments. It was expected that the cueing signal would reduce the uncertainty of Ss about the stimuli being presented in these experiments. In general, it was found that performance tended to improve as the experiments progressed, both in conditions in which cues were presented and in control conditions in which no cues were presented. The improvement observed in control conditions is not usually found in similar experiments in which cues are not employed. Though performance generally improved, it was found that for some stimulus conditions the cues tended to depress average performance below the level attained without such cues.     

A signal detection theory analysis of gap detection in the rat

An innocuous sensory event (a prestimulus) briefly preceding a startle-eliciting stimulus (SES) reduces the amplitude of the elicited reflex. This study used signal detection theory (SDT) techniques to quantify the effects of gaps (pauses in otherwise continuous noise) on the rat’s acoustic startle reflex. Sixteen rats were given four identical test sessions consisting of the randomized presentation of 150 trials of the SES alone and 150 trials of a gap-and-SES combination. Gap duration (1, 2, 4, and 8 msec) varied between sessions. Data analyses based on amplitude, difference scores, percentage scores, and SDT techniques identified similar patterns. The three longest gaps, but not the shortest, were reliably detected, and differences among these three were identified with percentage and SDT analyses. Analyses of amplitude changes over test sessions yielded different patterns for each measure. The results demonstrate that an SDT analysis is a sensitive index of prestimulus effects.     

Computer signal detection by monitoring auditory evoked potentials

A digital computer, using a simple decision algorithm, attempted to determine when an acoustical signal had been presented to a cat by monitoring the amplitude of the evoked potentials (EP) at brainstem auditory nuclei. The signal-to-noise level at threshold and the shape and range of the decision model “psychometric functions” were similar to those obtained from humans in the same task. In addition, the detection performance obeys Weber’s law, the mean amplitude of the EP increases monotmonically with signal level, the variance of the amplitude is independent of both signal and noise level, and both the mean latency and the variance of the latency of the peaks decrease with increasing signal level. These findings suggest that the synchronization in firing of a population of single units plays a part in determining the amplitude of the EP. Interaural effects in detection performance were found at the inferior colliculus and, to a lesser extent, at the superior olive.     

Speed-accuracy tradeoff models for auditory detection with deadlines

Two neural models for response latency in auditory signal detection are considered: the Timing model of Luce and Green (1972) and a modified counting model based on that of McGill (1967). The modified counting model is described in some detail. The experimental situation to which the models are applied is one where a deadline in response time is enforced on signal trials only or on noise trials only, the condition of deadlines on both cases having previously been studied by Green and Luce (1973). The results for mean latencies of the various categories of response, together with response probabilities, favour either the counting model or a dual process model. Data for ROC curves indicate either the operation of a dual process model or that the ‘interval of uncertainty’ of the counting model may vary with bias position. Some consideration is also given to the possibility of differential residual response time components and it is concluded that such components may be important in the deadline situation.     

Developmental perspectives on the localization and detection of auditory signals

Responsiveness of 1-, 3-, and 5-year-old children and adults to octave-band noises at .4 and 10 kHz was assessed with a go/no-go version of visual reinforcement audiometry (VRA) (Moore, Thompson, & Thompson, 1975) and a two-alternative, forced-choice version (Suzuki & Ogiba, 1961; Trehub, Schneider, & Endman, 1980). Infants performed better on the two-alternative, forced-choice version in quiet and in noisy backgrounds, and adults performed better on the two-alternative, forced-choice version in quiet but not in noisy backgrounds. Performance on the two tasks was essentially equivalent for 3- and 5-year-old children. Superior performance on two-alternative VRA over go/no-go may be due to lesser cognitive demands in the case of infants and to the engagement of superior decision strategies in the case of adults.     

Hemispheric asymmetries for gap detection depend on noise type

Studies of temporal processing asymmetries in the auditory modality have not produced consistent results. Some investigators have found a left hemisphere advantage, but others have failed to replicate this result. The present experiment investigated the possibility that differing properties of the noise employed between these experiments could be responsible for the conflicting results. Short bursts (300 ms) of white or brown noise were delivered monaurally to 42 participants. Half of the stimuli contained 3-5 ms gaps of silence. A right ear (left hemisphere) advantage in accuracy was observed in the white noise condition, but there was no such difference in the brown noise condition. This result demonstrates that the different acoustic properties of the stimuli between experiments can account for some of the discrepancies in their findings, and supports the position that the left hemisphere is superior at processing rapid temporal changes.     

Response latency,confidence, and ROCs in auditory signal detection

Response latencies were obtained from 10 Ss in auditory signal-detection experiments. The response latencies were inversely related to certainty that a signal was (or was not) presented. The S’s decision criterion was found to have an influence on response latency, which was consistent with the hypothesis that stimuli close to the current criterion elicit longer response latencies than stimuli more distant from the criterion. Comparisons among receiver operating characteristics derived from binary decisions, from the latencies of binary decisions, and from confidence ratings show that response latencies and binary decisions together yield more information about the stimulus than does the binary decision alone. However, the increment in information gained from the measurement of response latencies is in general (though not for every S) smaller than that gained by shifting from yes-no responses to a confidence-rating procedure.     

Influence of correlated visual cues on auditory signal detection

Two experiments investigated the effects on auditory signal detection of introducing visual cues that were partially correlated with the signal events. The results were analyzed in terms of a detection model that assumes that such cue-signal correlations will not affect sensitivity, but will instead cause the subject to develop separate response biases for each cue. The model specifies a functional relationship between the asymptotic values of these cuecontingent biases. The overall results of the experiments supported the detection assumptions of the model and the general bias learning assumption, but indicated a more complex learning process than that specified by the model.     

The detection of a temporal gap between two disparate stimuli

When a temporal gap is bounded by a light and a tone, gap detection performance as a function of gap duration is well described by a simple model which characterizes the discrimination as a purely temporal one. When the gap is bounded by two tones, performance is superior and seems to depend on the frequency difference between the tones, but is not well described by the same model. It is suggested that the light-tone performance represents the operation of a central temporal discrimination mechanism, while the tone-tone cases represent the use by Os of nontemporal cues originating in the peripheral auditory system.     

A deafening flash! Visual interference of auditory signal detection

In some people, visual stimulation evokes auditory sensations. How prevalent and how perceptually real is this? 22% of our neurotypical adult participants responded ‘Yes' when asked whether they heard faint sounds accompanying flash stimuli, and showed significantly better ability to discriminate visual ‘Morse-code’ sequences. This benefit might arise from an ability to recode visual signals as sounds, thus taking advantage of superior temporal acuity of audition. In support of this, those who showed better visual relative to auditory sequence discrimination also had poorer auditory detection in the presence of uninformative visual flashes, though this was independent of awareness of visually-evoked sounds. Thus a visually-evoked auditory representation may occur subliminally and disrupt detection of real auditory signals. The frequent natural correlation between visual and auditory stimuli might explain the surprising prevalence of this phenomenon. Overall, our results suggest that learned correspondences between strongly correlated modalities may provide a precursor for some synaesthetic abilities.     

Some models of observer behavior in two-channel auditory signal detection

Five models of 0 behavior in a two-channel exclusive-or (XOR) detection task were evaluated. The models included two types of single-channel and three types of two-channel O. Only the most efficient two-channel model adequately described human performance in a set of monaural and dichotic XOR conditions. Detectability measures derived from the XOR task matched those obtained from separate single-channel control conditions. We concluded that. in this two-channel task. the O’s performance was not limited by any inability to monitor signals arriving simultaneousl.v in two different earphone or two different frequency channels. The implications of this result for two-channel information processing and for multicomponent and sequential signal detectmn are discussed.