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.     

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.     

Efficient estimation of sensory thresholds

Laboratory computers permit detection and discrimination thresholds to be measured rapidly, efficiently, and accurately. In this paper, the general natures of psychometric functions and of thresholds are reviewed, and various methods for estimating sensory thresholds are summarized. The most efficient method, in principle, using maximum-likelihood threshold estimations, is examined in detail. Four techniques are discussed that minimize the reported problems found with the maximum-likelihood method. A package of FORTRAN subroutines, ML-TEST, which implements the maximum-likelihood method, is described. These subroutines are available on request from the author.     

Invariance of the psychometric function for character recognition across the visual field.

The psychometric function for recognition of singly presented digits as a function of digit contrast was measured at 2 degrees steps across the horizontal meridian of the visual field, under monocular and binocular viewing conditions. A maximum-likelihood staircase procedure was used in a 10-alternative forced-choice recognition paradigm to gather the data Both the Weibull and the logistic psychometric functions provide excellent fits to the observed data. The slopes of these functions at their point of inflection ranged from 4.0 to 5.0 proportion-correct/log10-unit contrast, for both monocular and binocular viewing and for all loci in the visual field. These slope values correspond to short-term measurements (around 30 trials, or 1 min) and do not include performance variations of longer duration; the latter are estimated to increase slope by a factor of about 1.5. A single psychometric function shape, centered around a threshold value, therefore describes recognition performance at all retinal loci and binocularity. An empirical comparison of slope results across the literature shows that the function's slope is about twice that reported for a number of detection tasks. The comparison of recognition contrast thresholds, percentage correct values, and other performance measures across studies requires the knowledge of the psychometric function's slope, and our results thus provide a firm basis for the study of low-contrast character recognition.     

An oblique effect of chromatic gratings measured by color-mixture thresholds

Contrast sensitivity is lower for obliquely oriented achromatic gratings than for vertical or horizontal gratings at high spatial and low temporal frequencies. Although this response is suggestive of mediation by P-pathway cortical correlates, no clear sensory (i.e. class 1) oblique effect has been demonstrated with isoluminant chromatic stimuli. In the present experiment, a two-alternative forced-choice detection task was used to measure observers' sensitivity to spatiotemporal sinusoids varying in orientation and color contrast. A maximum-likelihood method fit ellipses to the thresholds, with the length of each ellipse taken as a measure of chromatic contrast sensitivity at isoluminance, and the width as luminance contrast threshold. A chromatic oblique effect was observed at about 3 cycles deg-1 suggesting an orientation bias within the cortical stream conveying P-cell activity.     

Invariance of the psychometric function for character recognition across the visual field

The psychometric function for recognition of singly presented digits as a function of digit contrast was measured at 2° steps across the horizontal meridian of the visual field, under monocular and binocular viewing conditions. A maximum-likelihood staircase procedure was used in a 10-alternative forcedchoice recognition paradigm to gather the data. Both the Weibull and the logistic psychometric functions provide excellent fits to the observed data. The slopes of these functions at their point of inflection ranged from 4.0 to 5.0 proportion-correct/log₁₀-unit contrast, for both monocular and binocular viewing and for all loci in the visual field. These slope values correspond to short-term measurements (around 30 trials, or 1 min) and do not include performance variations of longer duration; the latter are estimated to increase slope by a factor of about 1.5. A single psychometric function shape, centered around a threshold value, therefore describes recognition performance at all retinal loci and binocularity. An empirical comparison of slope results across the literature shows that the function’s slope is about twice that reported for a number of detection tasks. The comparison of recognition contrast thresholds, percentage correct values, and other performance measures across studies requires the knowledge of the psychometric function’s slope, and our results thus provide a firm basis for the study of low-contrast character recognition     

Slope bias of psychometric functions derived from adaptive data.

Several investigators have fit psychometric functions to data from adaptive procedures for threshold estimation. Although the threshold estimates are in general quite correct, one encounters a slope bias that has not been explained up to now. The present paper demonstrates slope bias for parametric and nonparametric maximum-likelihood fits and for Spearman-K?rber analysis of adaptive data. The examples include staircase and stochastic approximation procedures. The paper then presents an explanation of slope bias based on serial data dependency in adaptive procedures. Data dependency is first illustrated with simple two-trial examples and then extended to realistic adaptive procedures. Finally, the paper presents an adaptive staircase procedure designed to measure threshold and slope directly. In contrast to classical adaptive threshold-only procedures, this procedure varies both a threshold and a spread parameter in response to double trials.     

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.     

Smoking and pain--a method of limits and sensory decision theory analysis

The effects of tobacco smoking on responses to electrical stimulation were studied according to a Method of Limits (ML) threshold analysis and a Sensory Decision Theory (SDT) analysis. For the ML procedure, Detection Threshold (DT), Pain Threshold (PT) and Tolerance Level (TL) measures were obtained. For the SDT procedure, nonparametric estimates of capacity to discriminate between stimulus intensities (P(A)) and response criterion (B) were calculated. There was no main effect of tobacco smoking on responses to electrical stimulation. Males had consistently higher ML thresholds than females in both the NS and S condition. Males also tended to increase in DT and PT after smoking. From a comparison between the effects of smoking on ML and SDT measures it was suggested that PT is related mainly to sensory factors and TL to response factors.     

Threshold variability in subliminal perception experiments: fixed threshold estimates reduce power to detect subliminal effects.

In studies of subliminal perception, a threshold for awareness is usually estimated for each S (e.g., the stimulus duration that yields chance discrimination performance). This article shows that if the S's true threshold varies randomly from trial to trial, estimation of a fixed threshold has important consequences. Specifically, the estimated threshold approaches the minimum of the distribution of true thresholds, and the power of an experiment to detect subliminal perception is reduced. Because there is much evidence that true thresholds vary across trials, threshold variability may have seriously weakened previous experiments that tested for subliminal perception. Fortunately, it is possible to estimate the maximum power loss resulting from threshold variability and therefore to design an experiment with acceptable power even in the presence of variability.     

Some task demands induce collapsing bounds: Evidence from a behavioral analysis

Traditional models of choice-response time assume that sensory evidence accumulates for choice alternatives until a threshold amount of evidence has been obtained. Although some researchers have characterized the threshold as varying randomly from trial to trial, these investigations have all assumed that the threshold remains fixed across time within a trial. Despite decades of successful applications of these models to a variety of experimental manipulations, the time-invariance assumption has recently been called into question, and a time-variant alternative implementing collapsing decision thresholds has been proposed instead. Here, we investigated the fidelity of the collapsing threshold assumption by assessing relative model fit to data from a highly constrained experimental design that coupled a within-subject mixture of two classic response time paradigms—interrogation and free response—within a random dot motion (RDM) task. Overall, we identified strong evidence in favor of collapsing decision thresholds, suggesting that subjects may adopt a dynamic decision policy due to task characteristics, specifically to account for the mixture of response time paradigms and motion strengths across trials in the mixed response signal task. We conclude that time-variant mechanisms may serve as a viable explanation for the strategy used by human subjects in our task.     

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.     

Slope bias of psychometric functions derived from adaptive data

Several investigators have fit psychometric functions to data from adaptive procedures for threshold estimation. Although the threshold estimates are in general quite correct, one encounters a slope bias that has not been explained up to now. The present paper demonstrates slope bias for parametric and nonparametric maximum-likelihood fits and for Spearman-Kärber analysis of adaptive data. The examples include staircase and stochastic approximation procedures. The paper then presents an explanation of slope bias based on serial data dependency in adaptive procedures. Data dependency is first illustrated with simple two-trial examples and then extended to realistic adaptive procedures. Finally, the paper presents an adaptive staircase procedure designed to measure threshold and slope directly. In contrast to classical adaptive threshold-only procedures, this procedure varies both a threshold and a spread parameter in response to double trials.     

Learning to allocate limited time to decisions with different expected outcomes

The goal of this article is to investigate how human participants allocate their limited time to decisions with different properties. We report the results of two behavioral experiments. In each trial of the experiments, the participant must accumulate noisy information to make a decision. The participants received positive and negative rewards for their correct and incorrect decisions, respectively. The stimulus was designed such that decisions based on more accumulated information were more accurate but took longer. Therefore, the total outcome that a participant could achieve during the limited experiments’ time depended on her “decision threshold”, the amount of information she needed to make a decision. In the first experiment, two types of trials were intermixed randomly: hard and easy. Crucially, the hard trials were associated with smaller positive and negative rewards than the easy trials. A cue presented at the beginning of each trial would indicate the type of the upcoming trial. The optimal strategy was to adopt a small decision threshold for hard trials. The results showed that several of the participants did not learn this simple strategy. We then investigated how the participants adjusted their decision threshold based on the feedback they received in each trial. To this end, we developed and compared 10 computational models for adjusting the decision threshold. The models differ in their assumptions on the shape of the decision thresholds and the way the feedback is used to adjust the decision thresholds. The results of Bayesian model comparison showed that a model with time-varying thresholds whose parameters are updated by a reinforcement learning algorithm is the most likely model. In the second experiment, the cues were not presented. We showed that the optimal strategy is to use a single time-decreasing decision threshold for all trials. The results of the computational modeling showed that the participants did not use this optimal strategy. Instead, they attempted to detect the difficulty of the trial first and then set their decision threshold accordingly.     

The statistical analysis of concurrent detection ratings

The concurrent detection task is a powerful method for assessing interactions in the processing of two sensory signals. On each trial, a stimulus is presented that is composed of one, both, or neither signal, and the observer makes a detection rating for each stimulus. A classical bivariate signal-detection analysis applies to these data, but is limited by its inability to differentiate certain types of sensory interactions from more cognitive components, and by the lack of an associated testing procedure. The present paper presents an alternative analysis, based on the contingency table of sensory ratings. Six classes of effect can be distinguished and tested: (1) simple response bias, (2) detection of the two signals, (3) interference of each signal on the response to the other signal, (4) sensory and response correlation, (5) bivariate response biases, and (6) higher order association. Complete computational detail is provided.     

Comparison of detection threshold values determined using glass sniff bottles and plastic squeeze bottles

Olfactory threshold measures are influenced by such factors as odorant species, diluent type, psychophysical paradigm, and stimulus-presentation procedure. In this study, we compared phenyl ethyl alcohol odor-detection thresholds obtained using 120-ml glass sniff bottles to those obtained using 120-ml plastic squeeze bottles. Although these presentation media are commonly employed in published studies, there has never been a formal comparison of values obtained using them. 10 male and 10 female subjects were tested on two threshold test sessions, one for each type of bottle. Order of sessions was systematically counterbalanced and completed on the same day for a given subject, with a minimum of 30 min. elapsing between sessions. A seven-reversal, single-staircase threshold procedure was employed. Although the threshold values were similar for the two procedures, slightly lower thresholds were obtained using the glass sniff bottles [respective M (SEM) log vol/vol values = -6.61 (.20) and -6.13 (.24)]. These data suggest that, while threshold values using these two presentation procedures can be roughly compared across studies, accurate comparisons may require a slight mathematical adjustment.     

Deterring malingered psychopathology: The effect of warning simulating malingerers

The utility of a warning to deter malingering on measures of personality and psychopathology was examined. Sixty‐seven first year psychology students were randomly assigned to one of three conditions: unwarned malingerers, warned malingerers, and controls. Participants in the two malingering groups were given a financial incentive to simulate believable psychological impairment. Warned malingerers received an additional warning that the tests could detect malingering and that detection would result in loss of course credit. Controls received standardized test instructions. It was hypothesized that the malingering incentive would be sufficient to induce malingering, but that a deterrence theory warning would have a subsequent deterrent effect. Between‐groups analyses indicated that the warning used in this study significantly altered test performance on the Personality Assessment Inventory (PAI) and revised Symptom Checklist 90 (SCL‐90‐R). Warned malingerers scored significantly lower (faked less) than unwarned malingerers on the majority of the psychopathology scales and frequently approximated control group performances. These results support the effectiveness of a warning to complement existing malingering detection methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Detection and placement of redundant signal elements in tachistoscopic displays of letters

On each trial of a forced-choice detection experiment, S indicated which of two signal elements was represented and also specified the cell of the 5 by 5 matrix display in which he detected the signal. Reaction time on correct choice, Correct placement trials proved virtually invariant with respect to number of redundant signal elements present in the display. These data do not support a serial model for sensory processing, but they could be accommodated by a parallel model for sensory processing together with a serial self-terminating model for processes involving comparison of elements of a display with items in memory. Further analyses of both frequency and reaction time data support the assumption that the distributions of observed detection response measures represent mixtures of true detections, guesses, and misperceptions.     

Threshold tracking for assessment of long-term adaptation and sensitization in pain perception

To assess temporal variations in the perception of "phasic" heat pain stimuli a psychophysical tracking procedure was developed that enables repeated assessment of the pain threshold at short intervals. This "double-tracking" procedure produces two tracking curves simultaneously, one that approaches the pain threshold gradually from above, the other from below. The threshold for phasic heat pain was measured in 80 tracking trials with stimuli at temperatures near the pain threshold. Concurrently, the threshold for "tonic" heat pain was determined after every 20 tracking trials with a stimulus adjustment procedure. Eleven healthy subjects (age: 26.4 yr. +/- 6.0) participated in 2 sessions each. Phasic stimulation near the pain threshold did not produce any trends in either of the two threshold measures. Hence there was no long-term adaptation or sensitization. However, there were random variations (random walks) in the tracking curves, which we interpret as resulting from a stochastic relationship between stimulus and sensation. In agreement with other reports, discrimination seemed to be better at painful than at nonpainful temperatures.