Auditory threshold,signal-to-noise ratio and signal detection theory

The use of Signal Detection Theory has demonstrated that there is not an auditory threshold at the level supposed by classical psychophysics, but has not disproved the existence of an auditory threshold at a lower level. Following the recommended signal detection theory procedure fairly closely, an experiment obtained evidence either of the existence of a signal-to-noise ratio audi tory threshold, or a nonlinear relationship between stimulus and response which could not be statistically distiguished from such a threshold , Using the same apparatus and subjects, audi tory thresholds were also obtained using the classical method of limits. The acoustic pressure for the classical thresholds was about five times as great as for the signal detection theory method.     

A threshold theory account of psychometric functions with response confidence under the balance condition

The study of thresholds for discriminability has been of long‐standing interest in psychophysics. While threshold theories embrace the concept of discrete‐state thresholds, signal detection theory discounts such a concept. In this paper we concern ourselves with the concept of thresholds from the discrete‐state modelling viewpoint. In doing so, we find it necessary to clarify some fundamental issues germane to the psychometric function (PF), which is customarily constructed using psychophysical methods with a binary‐response format. We challenge this response format and argue that response confidence also plays an important role in the construction of PFs, and thus should have some impact on threshold estimation. We motivate the discussion by adopting a three‐state threshold theory for response confidence proposed by Krantz (1969, Psychol. Rev., 76, 308–324), which is a modification of Luce's (1963, Psychol. Rev., 70, 61–79) low‐threshold theory. In particular, we discuss the case in which the practice of averaging over order (or position) is enforced in data collection. Finally, we illustrate the fit of the Luce–Krantz model to data from a line‐discrimination task with response confidence.     

Detecting malingerers by means of response-sequence analysis

The feigning of sensory loss (malingering) poses a challenge for psychophysicists. To uncover malingerers by means of psychophysical testing, we combined measures of response-sequence randomness with the maximum-likelihood adaptive-staircase procedure used to measure sensory detection thresholds. The two-alternative, forced-choice maximum-likelihood adaptive-staircase procedure calculates an estimate of the threshold after each trial and also recommends the stimulus concentration for the next trial. Olfactory detection thresholds for butyl alcohol were measured in 7 normals, 6 anosmics, and 6 malingerers. Each participant was tested for 20 trials. A discriminant analysis, using threshold concentration and probability of being correct over the 20 trials, could correctly classify only 68% of the malingerers and anosmics. Correct classification of anosmics and malingerers rose to 100% when statistical measures of randomness in the response sequences were included in the discriminant analysis. We conclude that the maximum-likelihood adaptive-staircase procedure, combined with response-sequence analysis, is a powerful addition to the arsenal of techniques for detecting malingerers in the evaluation of sensory ability.     

The effect of interstimulus procedures

NaCl detection and recognition thresholds were measured with and without a prior artificial raising of the level of adaptation by a molar salt mouthrinse. In both cases, it was found that an interstimulus procedure involving water mouthrinses yielded lower thresholds than a procedure with no rinses. These results were seen to be predicted from adaptation level changes. The literature was seen to confirm these results, while difficulties in threshold measurement were discussed.     

A comparison of three adaptive psychophysical procedures using inexperienced listeners

Thresholds for a masked 1-kHz tone were obtained in single sessions from 60 inexperienced listeners. A two-alternative forced-choice procedure was used in conjunction with one of three adaptive psychophysical techniques. These techniques comprised two staircase techniques targeting either 70.7% or 79.4% correct detection (Staircase-71 and Staircase-79), and parameter estimation by sequential testing (PEST), targeting 80% correct detection. Listeners were provided with a rationale for maintaining concentration at weak signal levels. Similar threshold values were obtained from the Staircase-79 and PEST groups in equal numbers of trials. The degree of oscillation in the level of the signal around the value finally chosen as the threshold was comparable for both staircase techniques. Subsequent fixed-level testing did not provide a true indication of the subjects' capabilities. The amount by which percent correct in fixed-level testing differed from expectations based on adaptive testing varied among the techniques. Additional thresholds were obtained in a second session from 30 of the original subjects. Thresholds with both staircase techniques improved by about 1 dB on retest, while thresholds with PEST were constant across sessions. The variability of the data compared well with that from studies involving experienced listeners.     

Sensory and non-sensory factors and the concept of externality in obese subjects

9 obese and 9 normal subjects performed a psychophysical task in which food- or non-food-related stimuli were briefly flashed tachistoscopically at a speed and intensity near the visual threshold. A signal was presented on one-half the trials and noise only on the other one-half of the trials. Using signal detection theory methodology, separate measures of sensory sensitivity (d') and response bias (beta) were calculated. No differences were noted between obese and normal subjects on measures of sensory sensitivity but significant differences on response bias. Obese subjects had consistently lower response criteria than normal ones. Analysis for subjects categorized by whether they were restrained or unrestrained eaters gave findings identical to those for obese and normal. The importance of using a methodology that separates sensory and non-sensory factors in research on obesity is discussed.     

Frequency selectivity using tonal-temporal masking: Diotic vs. dichotic masking

A combined forward-backward masking procedure was used to investigate the threshold of a 30-msec, 500-Hz signal as a function of masker frequency. The signal thresholds were obtained in two signal conditions, diotic (So) and dichotic (S_π), and for two different temporal separations of the maskers. The maskers were 500 msec in duration and were presented at 75 dB SPL. The function relating masked signal threshold to masker frequency was used to describe frequency selectivity in the four conditions. There were no differences in frequency selectivity measured between the diotic and dichotic signal conditions and only a small difference measured between the two intermasker interval conditions. The S_π conditions yielded lower thresholds than did the So conditions. The change in intermasker interval from 10 to 50 msec lowered the threshold maximally 18 dB for the So condition and 13 dB for the S_π condition. The results indicate that in this tonal temporal masking procedure there are no differences between the diotic and dichotic critical bands.     

Simultaneous behavioral and neural (cochlear nucleus) measurement during signal detection in the rabbit

Classical conditioning of the rabbit nictitating membrane (NM) response was adapted as a model system for simultaneous measurement of behavioral and neural responses in auditory signal detection. Animals were trained to a 36-dB spectral-level white-noise CS paired with a corneal airpuff US. The CS intensity was then reduced to threshold, using a modified staircase procedure, and responses on detect and nondetect trials were compared for the same stimulus intensities. At threshold, the behavioral NM response was dichotomous, being present on detect trials and completely absent on nondetect trials. In marked contrast, evoked neural unit activity to the CS recorded from the anteroventral cochlear nucleus was clearly present and identical on both detect and nondetect trials, suggesting that the detection “decision” is made more centrally than the cochlear nucleus.     

Evaluation of maximum-likelihood estimators in nonintensive auditory psychophysics

This is a brief report on the use of maximum-likelihood (ML) estimators in auditory psychophysics. Slope parameters of psychometric functions are characterized for three nonintensive auditory tasks: forced-choice discrimination of interaural time differences (ΔITD), frequency (Δf), and duration (Δt). Using these slope estimates, the ML method is implemented and threshold estimates are obtained for the three tasks and compared with previously published data. ΔITD thresholds were additionally measured for human observers by means of two other psychophysical procedures: the constant-stimuli (CS) and the 2-down 1-up methods (Wetherill & Levitt, 1965). Standard errors were smallest for the ML method. Finally, simulations showed ML estimates to be more efficient than the CS andk-down 1-up procedures fork=2 to 5. For up—down procedures, efficiency was highest fork values of 3 and 4. The entropy (Shannon, 1949) of ML estimates was the smallest of the simulated procedures, but poorer than ideal by 0.5 bits.     

Administrative Assumptions in Top‐Down Selection: A Test in Graduate School Admission Decisions

Although top‐down selection is the gold standard for making personnel decisions, several administrative assumptions must be met for it to be effective. We discuss three of these assumptions and test two of them: (1) top applicants will accept an offer, and (2) the time organisations give applicants to consider an offer will not influence the availability of next‐tier applicants. We also examine the effectiveness of top‐down selection by comparing it to an administratively simpler procedure, random selection above a threshold. Using archival admissions data from three university graduate psychology programs, we found that top applicants were less likely to accept an offer; however, waiting time did not influence applicant availability. In comparing the quality of applicants actually selected (with a top‐down procedure) with the quality of applicants selected at random (from above five progressively stringent thresholds), we found that at higher admission thresholds, random selection resulted in better or equal quality applicants as top‐down selection, depending on the criteria. We discuss implications for future research and practice.     

Differential thresholds for limb movement measured using adaptive techniques

Differential thresholds for limb movement were measured in 10 subjects, using the transformed up-down procedure. Subjects were required to indicate which of two random displacement perturbations delivered to their forearms had the larger standard deviation (SD). TheSD of the reference signal was fixed for each experimental condition at one of seven values ranging from 0.05 to 3.2 mm. TheSD of the other signal varied depending on the subject’s response. Using this procedure, the differential threshold for limb movement was calculated to be 8%, which is very similar to the thresholds estimated previously for changes in limb position (9%) and force (7%). The sensitivity of the human proprioceptive system to changes in limb displacement was much greater than anticipated, with subjects being able to resolve a 5-μm difference between two perturbations delivered to their arms.     

Unconscious perception or not? An evaluation of detection and discrimination as indicators of awareness

Most investigations of unconscious perception use a dissociation design in which an awareness variable (e.g., detection) is compared with a perceptual processing variable (e.g., identification). Unconscious perception is inferred when the awareness variable lacks sensitivity to the stimulus but evidence of perceptual processing is still obtained. In two studies we examined the relationship between word identification and detection (Study 1) or discrimination (words vs. nonwords; Study 2) with a variety of techniques. In both studies, dissociations suggestive of unconscious perception occurred when the data were examined with subjective threshold approaches, but these differences disappeared when the variables were compared with techniques derived from signal detection theory (SDT). These results do not support unconscious perception in subjective threshold paradigms. In addition, detection appears to be the most sensitive and appropriate task for assessing stimulus awareness, provided that several SDT assumptions are met.     

Detection by the guinea pig of acoustic stimulation and of electrical stimulation of the brain

A threshold procedure using operant behavioral techniques with positive reinforcement was developed after initial efforts with avoidance behavioral procedures proved unsatisfactory. In the first of three experiments the operant threshold procedure was tested by determining masked auditory thresholds for trains of clicks. In a second experiment, similar techniques were used to measure thresholds for electrical stimulation of the brain. The last experiment, again an auditory problem, involved a determination of the absolute thresholds for trains of short noise bursts as a function of the time between bursts. Middle ear malfunction proved to be a more severe problem than had been anticipated on the basis of reports in the literature. The threshold procedure, however, seems to be adequate for determination of absolute or masked thresholds with auditory or electrical stimuli.     

Differential thresholds for limb movement measured using adaptive techniques.

Differential thresholds for limb movement were measured in 10 subjects, using the transformed up-down procedure. Subjects were required to indicate which of two random displacement perturbations delivered to their forearms had the larger standard deviation (SD). The SD of the reference signal was fixed for each experimental condition at one of seven values ranging from 0.05 to 3.2 mm. THe SD of the other signal varied depending on the subject's response. Using this procedure, the differential threshold for limb movement was calculated to be 8%, which is very similar to the thresholds estimated previously for changes in limb position (9%) and force (7%). The sensitivity of the human proprioceptive system to changes in limb displacement was much greater than anticipated, with subjects being able to resolve a 5-microns difference between two perturbations delivered to their arms.     

Frequency selectivity in the parakeet (Melopsittacus undulatus) studied with psychophysical tuning curves

Seven parakeets were trained to avoid shock during pure-tone stimulation. A modified method of limits was used to measure detection thresholds of the pure tones. The intensity of masker tones, at numerous frequencies, was varied in order to measure the masked threshold of a probe-tone signal set at a fixed frequency and intensity. Masking curves were obtained for three probe tones (.63, 1.6, and 2.5 kHz) at each of five sensation levels (10, 20, 30, 40, and 50 dB). The masking curves from this procedure are frequently referred to as "psychophysical tuning curves" and provide an indication of frequency selectivity. The results are compared with analogous data in other species and suggest that frequency analysis in the parakeet ear is somewhat less accurate than in the mammalian ear.     

The detectability of the odor of butanol

Three experiments were conducted to measure the sensitivity of two Ss to the odor of butanol. In the first two experiments, the method of double random, yes-no staircases was used. A practice effect of over a log₁₀ unit in millimoles decrease in apparent threshold was observed in both Ss. Consistent shifts in the response criterion were induced when Ss were paid to meet an arbitrarily determined physical criterion. In Experiment S, the confidence rating procedure was used. Results at eight different signal intensities are of the form predicted by signal detection theory. d’ is shown to be related to signal strength by a power function with a slope of about .30 which suggests that the olfactory transducer compresses sensory input produced by weak concentrations of butanol.     

An Examination of Sex and Masculinity/Femininity as Related to the Taste Sensitivity of Japanese Students

The purpose of the present study was to examine the influences of gender differences and masculinity–femininity on taste thresholds and food preferences. The participants were 108 Japanese undergraduate students (44 men and 64 women); their mean age was 19.6 years (SD = 1.3). Their detection and recognition thresholds for caffeine and sucrose were measured. Multiple regression analyses showed that women tended to have a lower detection threshold for caffeine than men did. The recognition threshold for caffeine was positively associated with scores for masculinity. For men, masculinity may be associated with smoking and drinking behavior, thereby resulting in a lower sensitivity for bitterness. Masculinity and femininity related to food preferences are also discussed.     

Using the PLUM procedure of SPSS to fit unequal variance and generalized signal detection models

The recent addition of a procedure in SPSS for the analysis of ordinal regression models offers a simple means for researchers to fit the unequal variance normal signal detection model and other extended signal detection models. The present article shows how to implement the analysis and how to interpret the SPSS output. Examples of fitting the unequal variance normal model and other generalized signal detection models are given. The approach offers a convenient means for applying signal detection theory to a variety of research.     

Rhesus monkey (Macaca mulatta) cool sensitivity measured by a signal detection method

Two rhesus monkeys were trained to detect cool stimuli (decrements in skin temperature from the adapted temperature) presented to the palm of the left hand after the skin had been preadapted to a 33°C temperature. The procedure was analogous to the signal detection “yes-no” method used with human observers. Receiver operating characteristic curves were generated by varying the a priori probability of stimulus oecurrence. The proportion of hits and of false alarms increased with increases in the a priori probability of stimulation. The points of isosensitivity of both subjects for cool intensities of 0.3°C, but not at greater intensities, yielded straight lines with slopes of approximately one when plotted on normal-normal coordinates. The values of the d’_s detectability index decreased from 3.52 to 0.75 for one subject and from 2.81 1to 1.28 for the other as the stimulus intensity was decreased from 0.8° to 0.15° cooling from the adapting temperature. Cool thresholds for each subject of 0.19° and 0.12°C were computed from classical psychometric functions when threshold was defined as 50% hits at a 50% probability of stimulus occurrence. These thresholds are comparable to published reports of the cool threshold for the rhesus.     

Perception of surface reflectance of 3-D geometrical shapes: influence of the lighting mode

We examined in three experiments whether the perception of surface reflectance in 3-D geometrical shapes is influenced by the mode of lighting, the level of surface reflectance, the number of polyhedral faces, and the regularity of polyhedral shape. As stimuli, we used simulations of regular polyhedra in a 2AFC constant-stimuli procedure to measure how large variations in the reflectance needed to be for observers to be able to tell whether the whole surfaces were uniform or non-uniform. In almost all the cases observers were more successful in discriminating non-uniform polyhedra in the hemispherical diffuse lighting conditions than in the collimated lighting conditions. The different levels of reflectance had no effect on the discrimination of non-uniformity. Second, as the number of faces of the shape increased, discrimination thresholds became lower, indicating that the interpretation of reflectance variations was better when a shape had many faces. Finally, the regularity of the shape, such as the central symmetry, was not an important factor. These results suggest that the interpretation of surface reflectance is more precise when surfaces have less variance in relative strengths between the face luminance values; these surfaces were the ones obtained under hemispherical diffuse lighting.