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.     

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.     

Simultaneous switching of auditory transients For two-channel presentation

A modification of the Grason-Stadler Series 829 D&E Electronic Switches that enables simultaneous cross-channel presentation of auditory signals at the two ears is described.     

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.     

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.     

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.     

Visual facilitation of auditory localization in schoolchildren: A signal detection analysis

Warren (1970) has claimed that there are visual facilitation effects on auditory localization in adults but not in children. He suggests that a “visual map” organizes spatial information and that considerable experience of correlated auditory and visual events is necessary before normal spatial perception is developed. In the present experiment, children in Grades 1, 4, and 7 had to identify the position, right or left, of a single tone either blindfolded or with their eyes open. Analysis of the proportion of area under the ROC curve (obtained using reaction times) in the respective conditions showed that Ss were more sensitive to auditory position when vision was available. Reaction time was also generally faster in the light. I argue that the increase in sensitivity in the light represents updating of auditory position memory by voluntary eye movement. In the dark, eye movements are subject to involuntary and unperceived drift, which would introduce noise into the eye control mechanism and hence into auditory spatial memory.     

Effect of subliminal visual material on an auditory signal detection task

An experiment assessed the effect of subliminally embedded, visual material on an auditory detection task. 22 women and 19 men were presented tachistoscopically with words designated as "emotional" or "neutral" on the basis of prior GSRs and a Word Rating List under four conditions: (a) Unembedded Neutral, (b) Embedded Neutral, (c) Unembedded Emotional, and (d) Embedded Emotional. On each trial subjects made forced choices concerning the presence or absence of an auditory tone (1000 Hz) at threshold level; hits and false alarm rates were used to compute non-parametric indices for sensitivity (A') and response bias (B"). While over-all analyses of variance yielded no significant differences, further examination of the data suggests the presence of subliminally "receptive" and "non-receptive" subpopulations.     

Vertex potentials evoked during auditory signal detection: Relation to decision criteria

Vertex potentials were recorded from eight Ss performing in an auditory threshold detection task with rating scale responses. The amplitudes and latencies of both the N1 and the late positive (P3) components were found to vary systematically with the criterion level of the decision. These changes in the waveshape of the N1 component were comparable to those produced by varying the signal intensity in a passive condition, but the late positive component in the active task was not similarly related to the passively evoked P2 component. It was suggested that the N1 and P3 components represent distinctive aspects of the decision process, with N 1 signifying the quantity of signal information received and P3 reflecting the certainty of the decision based upon that information.     

Visual laterality effects: A signal detection analysis

Subjects were asked to indicate, by a simple motor response, the presence or absence of a pre-designated target letter in unilaterally presented consonant trigrams. For horizontally oriented stimuli (Experiment 1), perceptual sensitivity was greater in the right visual hemifield. For vertically oriented stimuli (Experiment 2), perceptual sensitivity did not differ between visual hemifields. Decision making was less conservative and reaction time was shorter with right hemifield presentation, regardless of stimulus orientation. Practice effects and serial position curves were examined. Implications of these results attribute laterality effects to iconic scanning patterns and to postperceptual decision processes.     

Decision-related cortical potentials during an auditory signal detection task with cued observation intervals.

Cortical-evoked potentials were recorded from human subjects performing an auditory detection task with confidence rating responses. Unlike earlier studies that used similar procedures, the observation interval during which the auditory signal could occur was clearly marked by a visual cue light. By precisely defining the observation interval and, hence, syncrhonizing all perceptual decisions to the evoked potential averaging epoch, it was possible to demonstrate that high-confidence false alarms for accompanied by late-positive P3 components equivalent to those for equally confident hits. Moreover the hit and false alarm evoked potentials were found to covary similarily with variations in confidence rating and to have similar amplitude distributions over the scalp. In a second experiment wherein the signal intensity was increased to make signal presence and signal absence clearly discriminable and the a priori probability of signal presentation was varied from .5 to .9, it was demonstrated that correct rejections can be associated with a P3 component larger than that for hits. Thus it was possible to show, within the signal detection paradigm, how the two major factors of decision confidence and expectancy are reflected in the P3 component of the cortical-evoked potential.     

Visual signal detection and the locus of foreperiod effects

The effect of alertness on S's sensitivity to external signals was determined by varying the foreperiod in a visual signal detection task. Discriminability increased with increasing foreperiods up to an optimal foreperiod, beyond which it decreased slightly. This pattern of results parallels closely that of many foreperiod studies in which reaction time was the dependent variable. Because no speeded response was required in this signal detection task, it was concluded that alertness must be affecting an information processing stage prior to those associated with responding. Other evidence indicates that alertness does not affect sensory stages either. Alertness, by elimination, must be affecting the operation of a central stage, Posner's view of alertness which implicates the central stages is discussed.     

The effect of psychological stress and expectation on auditory perception: A signal detection analysis

Both psychological stress and predictive signals relating to expected sensory input are believed to influence perception, an influence which, when disrupted, may contribute to the generation of auditory hallucinations. The effect of stress and semantic expectation on auditory perception was therefore examined in healthy participants using an auditory signal detection task requiring the detection of speech from within white noise. Trait anxiety was found to predict the extent to which stress influenced response bias, resulting in more anxious participants adopting a more liberal criterion, and therefore experiencing more false positives, when under stress. While semantic expectation was found to increase sensitivity, its presence also generated a shift in response bias towards reporting a signal, suggesting that the erroneous perception of speech became more likely. These findings provide a potential cognitive mechanism that may explain the impact of stress on hallucination‐proneness, by suggesting that stress has the tendency to alter response bias in highly anxious individuals. These results also provide support for the idea that top‐down processes such as those relating to semantic expectation may contribute to the generation of auditory hallucinations.     

The effects of aging on reaction time in a signal detection task

The effects of aging on response time are examined in 2 simple signal detection tasks with young and older subjects (age 60 years and older). Older subjects were generally slower than young subjects, and standard Brinley plot analyses of response times showed typical results: slopes greater than 1 and (mostly) negative intercepts. R. Ratcliff, D. Spieler, and G. McKoon (2000) showed that the slopes of Brinley plots measure the relative standard deviations of the distributions of response times for older versus young subjects. Applying R. Ratcliff's (1978) diffusion model to fit the response times, their distributions, and response accuracy, it was found that the larger spread in older subjects' response times and their slowness relative to young subjects comes from a 50-ms slowing of the nondecision components of response time and more from conservative settings of response criteria.     

Vibrotactile signal detection

The theory of signal detectability was applied to vibrotactile sensitivity in two experiments. The first experiment showed The psychometric function to be satisfactorily linear when a sensitivity index of the d family was plotted against the signal intensity expressed in decibels. The second experiment yielded receiver-operating-characteristic (ROC) curves of a familiar form for the yes-no and rating response methods. Reasonably consistent estimates of sensitivity were obtained in the second experiment from the yes-no. rating, and forced-choice methods. The sensitivity indices examined were d’ and d_e’, based on Gaussian density functions; A, based on Rayleigh density functions; and the distribution-free indices, P(A) and F(C). For each type of index a tendency was observed for the forced-choice value to be lower than the yes-no and rating values.     

Spreadsheet signal detection

A number of studies in perception, attention, and memory employ signal detection theory (SDT) to assess the accuracy of an observer’s detection or discrimination performance. Some of the problems that students have with understanding and using SDT are associated with the calculations needed to obtain SDT parameters and predictions. All of these calculations, plus the simulation of SDT processes, can be performed using a spreadsheet application program, such as Excel or Quattro Pro. This paper offers a short tutorial on how to use a spreadsheet program to increase your students’ knowledge and understanding of SDT.