PESTI: A procedure for estimating individual thresholds in infant listeners

An adaptive procedure for rapid estimation of adult thresholds (PEST: Parameter Estimation by Sequential Testing; Taylor & Creelman, 1967) was modified and applied to the estimation of auditory thresholds in 6-month-old infants (PESTI). This procedure yielded similar absolute thresholds to those obtained in previous research with the method of constant stimuli. Advantages of the present procedure are outlined.     

The single interval adjustment matrix (SIAM) yes–no task: an empirical assessment using auditory and gustatory stimuli

The SIAM yes-no task is an efficient bias-free adaptive procedure for estimating absolute thresholds, though it arguably requires further evaluation prior to its adoption into mainstream psychological research. We report two experiments undertaken in the auditory and gustatory modalities designed to assess the accuracy and efficiency of the SIAM method. In the first experiment, estimates of absolute thresholds for 1000-Hz tones obtained using a two-alternative forced choice adaptive procedure were compared to those obtained using both the SIAM yes-no task and a modification of the SIAM task incorporating the method of free response, the SIAM-rapid. In Experiment 2, we compared absolute thresholds for sucrose in solution obtained with either a two-alternative forced choice adaptive procedure or the SIAM yes-no task. Both experiments demonstrated the efficiency and validity of the SIAM approach, with SIAM thresholds proving to be equivalent to those obtained in the two-alternative forced choice tasks and to those reported in the literature.     

Naturalistic psychophysics: thresholds of ducklings (Anas platyrynchos) and chicks (Gallus gallus) to tones that resemble mallard calls

Neonatal ducklings and chickens were tested for responsiveness to a pulsing pure tone that was as similar as possible to the mallard maternal alarm call. It is known that ducklings momentarily cease vocalizing when they hear the alarm call and that chicks do the same when they hear pure tones. The duration of peep suppression can thus be used as a measure of whether subjects of either species heard the stimulus. Chicks might not be as sensitive as ducklings to a mallard alarm call because the signal is less significant to them. An adaptive or staircase procedure was used to estimate absolute thresholds, and group psychometric functions were reconstructed for each species from the trial-by-trial data. Ducklings had lower thresholds than chickens as well as steeper psychometric functions to this stimulus. The results suggest that more sensitive and consistent behavioral responses can be elicited by naturalistic sounds than by more arbitrary acoustic stimuli.     

Fast and accurate measurement of taste and smell thresholds using a maximum-likelihood adaptive staircase procedure.

This paper evaluates the use of a maximum-likelihood adaptive staircase psychophysical procedure (ML-PEST), originally developed in vision and audition, for measuring detection thresholds in gustation and olfaction. The basis for the psychophysical measurement of thresholds with the ML-PEST procedure is developed. Then, two experiments and four simulations are reported. In the first experiment, ML-PEST was compared with the Wetherill and Levitt up-down staircase method and with the Cain ascending method of limits in the measurement of butyl alcohol thresholds. The four Monte Carlo simulations compared the three psychophysical procedures. In the second experiment, the test-retest reliability of MLPEST for measuring NaCl and butyl alcohol thresholds was assessed. The results indicate that the ML-PEST method gives reliable and precise threshold measurements. Its ability to detect malingerers shows considerable promise. It is recommended for use in clinical testing.     

Fast and accurate measurement of taste and smell thresholds using a maximum-likelihood adaptive staircase procedure

This paper evaluates the use of a maximum-likelihood adaptive staircase psychophysical procedure (ML-PEST), originally developed in vision and audition, for measuring detection thresholds in gustation and olfaction. The basis for the psychophysical measurement of thresholds with the ML-PEST procedure is developed. Then, two experiments and four simulations are reported. In the first experiment, ML-PEST was compared with the Wetherill and Levitt up-down staircase method and with the Cain ascending method of limits in the measurement of butyl alcohol thresholds. The four Monte Carlo simulations compared the three psychophysical procedures. In the second experiment, the test-retest reliability of ML-PEST for measuring NaCl and butyl alcohol thresholds was assessed. The results indicate that the ML-PEST method gives reliable and precise threshold measurements. Its ability to detect malingerers shows considerable promise. It is recommended for use in clinical testing.     

Aging and temporal discrimination of brief auditory intervals

Summary In a duration-discrimination experiment, young adults (mean age = 25.1), middle-aged adults (mean age = 45.5), and older adults (mean age = 64.6) were presented with two very brief auditorily marked intervals per trial, and their task was to decide which of the two was longer in duration. An adaptive psychophysical procedure was used to determine difference thresholds in relation to a constant standard interval of 50 ms. It was found that duration-discrimination performance was unaffected by age; all three age groups yielded a difference threshold of approximately 17 ms. It was concluded that the ability to discriminate durations of very brief auditory intervals appears to be based on an underlying timing mechanism that does not slow down with advancing adult age.     

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.     

Coherence masking protection for speech in children and adults

In three experiments, we tested the hypothesis that children are more obliged than adults to fuse components of speech signals and asked whether the principle of harmonicity could explain the effect or whether it is, instead, due to children's implementing speech-based mechanisms. Coherence masking protection (CMP) was used, which involves labeling a phonetically relevant formant (the target) presented in noise, either alone or in combination with a stable spectral band (the cosignal) that provides no additional information about phonetic identity and is well outside the critical band of the target. Adults and children (8 and 5 years old) heard stimuli that were either synthetic speech or hybrids consisting of sine wave targets and synthetic cosignals. The target and cosignal either shared a common harmonic structure or did not. An adaptive procedure located listeners' thresholds for accurate labeling. Lower thresholds when the cosignal is present indicate CMP. Younger children demonstrated CMP effects that were both larger in magnitude and less susceptible to disruptions in harmonicity than those observed for adults. The conclusion was that children are obliged to integrate spectral components of speech signals, a perceptual strategy based on their recognition of when all components come from the same generator.     

Operant methods for mouse psychoacoustics

Tone detection thresholds for a 10-kHz tone in NMRI mice were determined in psychoacoustic experiments using both a constant-stimuli procedure and a two-down/one-up adaptive-tracking procedure in the same subjects and applying identical threshold criteria (70.7% response probability). Constant-stimuli thresholds were on average 24 dB lower than adaptive-tracking thresholds, and there was a trend indicating that constant-stimuli thresholds were less variable than adaptive-tracking thresholds. Furthermore, in the constant-stimuli procedure the number of trials constituting the psychometric function could be reduced from 100 to 50 trials without a large loss of accuracy of threshold determination. In the constant-stimuli procedure, the threshold value was affected by the threshold criteria. The lowest and least variable constant-stimuli thresholds were obtained by applying signal detection theory and a criterion ofd′=1. Thus, the constant-stimuli procedure in combination with signal detection theory appears to be better suited than the adaptive-tracking procedure to determine auditory sensory thresholds.     

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.     

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.     

Tracking of nociceptive thresholds using adaptive psychophysical methods

Psychophysical thresholds reflect the state of the underlying nociceptive mechanisms. For example, noxious events can activate endogenous analgesic mechanisms that increase the nociceptive threshold. Therefore, tracking thresholds over time facilitates the investigation of the dynamics of these underlying mechanisms. Threshold tracking techniques should use efficient methods for stimulus selection and threshold estimation. This study compares, in simulation and in human psychophysical experiments, the performance of different combinations of adaptive stimulus selection procedures and threshold estimation methods. Monte Carlo simulations were first performed to compare the bias and precision of threshold estimates produced by three different stimulus selection procedures (simple staircase, random staircase, and minimum entropy procedure) and two estimation methods (logistic regression and Bayesian estimation). Logistic regression and Bayesian estimations resulted in similar precision only when the prior probability distributions (PDs) were chosen appropriately. The minimum entropy and simple staircase procedures achieved the highest precision, while the random staircase procedure was the least sensitive to different procedure-specific settings. Next, the simple staircase and random staircase procedures, in combination with logistic regression, were compared in a human subject study (n = 30). Electrocutaneous stimulation was used to track the nociceptive perception threshold before, during, and after a cold pressor task, which served as the conditioning stimulus. With both procedures, habituation was detected, as well as changes induced by the conditioning stimulus. However, the random staircase procedure achieved a higher precision. We recommend using the random staircase over the simple staircase procedure, in combination with logistic regression, for nonstationary threshold tracking experiments.     

Discrimination of restrictions in sequentially-encoded auditory displays: Block designs

Sequential constraints, in the form represented by equal frequencies within blocks, were imposed upon finite-state statistical generators. The sequences were encoded in the form of interval-coded pulse trains and were transduced to sound by earphones. In discrimination tests, interval thresholds between the finite states provided a measure of the relative discriminability between different sequential constraints. These thresholds are shown to be quantitatively related to the difference in uncertainty in specification of the sequences. To a first approximation: Equal interstate interval thresholds are associated with equal differences in uncertainty.     

Tolerance of pain as a measure of fear

Fear thresholds were measured in four experiments by exposing rats to electric shock in order to determine the maximal intensity rats would tolerate rather than enter a fear-arousing box and/or stop freezing. Increasing fear raised these thresholds. They were greater for rats having to escape shock to a fear-arousing box than for rats having to escape shock and fear to a neutral box. The forgetting functions for the latter two groups differed: the first group yielded a monotonic decay function, whereas the second group yielded an inverted U-shaped function. These thresholds decreased as a function of an avoidance learning procedure. Rats that had to escape shock to a fear arousing box did not do so immediately, although they had stopped freezing. An avoidance-avoidance conflict explanation for immobility was not found to be valid. A theoretical formulation based on the following two hypotheses was suggested to explain these results: the fear-aroused freezing (immobility) is an unlearned response; finding a way to escape the source of fear starts another unlearned response, withdrawal.     

Tempo sensitivity in auditory sequences: Evidence for a multiple-look model

Differential thresholds for tempi (with interonset intervals ranging from 100 to 1,500 msec) were measured using an adaptive 2IFC paradigm for several types of auditory sequences. In Experiment 1, the number of intervals in an isochronous sequence was varied to compare the sensitivity for single intervals withthat for sequences of two to six intervals. Mean relative just noticeable differences (JNDs) decreased as the number of intervals increased (single intervals=6%, two intervals=4%, four intervals=3.2%, six intervals=3%) and were optimal at intermediate tempi for both sequences and single intervals (as low as 1.5% in the range between 300 and 800 msec). In Experiment 2, the sensitivity for different types of irregular sequences was studied. Globally, JNDs for irregular sequences were of an intermediate level between that observed for single intervals and that observed for regular sequences. However, the closer a sequence was to regularity, the lower its relative JND. Experiment 3 demonstrated that musicians were more sensitive than nonmusicians to changes in tempo, and this was true for single intervals and for regular and irregular sequences, demonstrating the role of training on these abilities. The results are discussed in terms of possible underlying mechanisms, in particular those providing a mental representation of the mean and dispersion of successive interval durations.     

Adaptive threshold estimation with unforced-choice tasks.

This paper evaluates an adaptive staircase procedure for threshold estimation that is suitable for unforced-choice tasks-ones with the additional response alternative don't know. Within the framework of a theory of indecision, evidence is developed that fluctuations of the response criterion are much less detrimental to unforced-choice tasks than to yes/no tasks. An adaptive staircase procedure for unforced-choice tasks is presented. Computer simulations show a slight gain in efficiency if don't know responses are allowed, even if response criteria vary. A behavioral comparison with forced-choice and yes/no procedures shows that the new procedure outdoes the other two with respect to reliability. This is especially true for naive participants. For well-trained participants it is also slightly more efficient than the forced-choice procedure, and it produces a smaller systematic error than the yes/no procedure. Moreover, informal observations suggest that participants are more comfortable with unforced tasks than with forced ones.     

Binaural loudness matches in unilaterally impaired listeners

Binaural loudness matching data using a 2IFC adaptive procedure were obtained in high-frequency, unilateral cochlear-impaired listeners. The matches were obtained at frequencies where both ears had similarly normal thresholds, and also at other frequencies where the impaired ear had various degrees of hearing loss. In these listeners, one presumed difference between the ears is the limited or altered spread of excitation in the impaired ear. In agreement with previous studies using other approaches (Hellman, 1974, 1978; Hellman & Meiselman, 1986; Moore, Glasberg, Hess & Birchall, 1985; Schneider & Parker, 1987), the results of the present study suggest that both the range and the slope of loudness growth function are not dependent on the spread of excitation, but instead are related primarily to the degree of threshold elevation at the test frequency. Following this suggestion, a spread-of-excitation-independent model, based upon a group of neurons with the same characteristic frequency (CF) but different thresholds, is proposed to account for loudness growth in both normal and recruitment cases. In particular, it is shown quantitatively that a compressed distribution of thresholds due to threshold elevation may be responsible for loudness recruitment in sensorineural hearing loss.     

Computer automation of biofeedback training

A computer-automated system has been developed for implementing response-contingent training strategies in EMG biofeedback-assisted relaxation training. An on-line minicomputer is programmed to (1) monitor progress within a training session as reflected in EMG signals; (2) compare the progress data with criteria set by the operator at the beginning of the session; and (3) on the basis of these comparisons, periodically adjust feedback gain (sensitivity) and make changes in the within-session training sequence. The system is designed to allow various adaptive training strategies to be software programmable. One of these strategies, a “shaping” procedure commonly employed in EMG biofeedback training, gradually increases the degree of relaxation necessary to produce the desired feedback signal by increasing feedback gain as the subject gets better at relaxing. Implementation of the shaping procedure is described as an illustration of system function. Current system development is guided by principles from adaptive testing and teaching systems to make more of the feedback training process adaptive in function.