Adaptive Psychometric Procedure Research Articles

Reflexive Saccades Used for Objective and Automated Measurements of Contrast Sensitivity in Selected Areas of Visual Field

PurposeThis study proposes a novel approach for objective and automated peripheral contrast sensitivity (CS) testing using reflexive saccades. Here the CS was examined in various areas the of visual field (VF) using a live analysis of gaze data. For validation of the new test, we examined CS with an established procedure of identifying the orientation of a contrast stimulus.MethodsTo perform and validate the saccade-based testing, two separate measurement events were performed. In the first, participants were asked to execute a saccade toward a newly-appeared stimulus in their VF. After the saccade execution or stimulus expiry, reporting the target orientation was required in a four-alternatives forced choice (4AFC). Therefore the first measurement yields two outcomes (objective and subjective). In the second measurement, only the identification of the stimulus orientation was requested, while fixating a central mark. Stimulus contrast was controlled by an adaptive psychometric procedure in both measurements.ResultsThe study found strong correlations (all r ≥ 0.79) of CS values for all three possible testing methods (saccade-based responding in saccadic measurements, keyboard-based responding in saccadic measurements, keyboard-based responding in non-saccadic measurements), showing the feasibility of employment of reflexive saccades in such testing. Second, this study shows a significant influence of eccentricity and direction of the stimulus on the CS function.ConclusionsCS measured with reflexive saccades is comparable to other testing methods over several areas of the participant's VF. Hence, we propose it as a novel and objective testing procedure for CS measurements.Translational RelevanceAssessment of CS using reflexive saccades extends the portfolio of suggested eye movement-based tests, allowing objective examination across the VF, which might be helpful especially in the early detection of various eye diseases.

Contrast Sensitivity Testing in Healthy and Blurred Vision Conditions Using a Novel Optokinetic Nystagmus Live-Detection Method

PurposeThe aim of the current study was to develop and validate an automated contrast sensitivity (CS) test using a live- detection of optokinetic nystagmus (OKN) and an adaptive psychometric procedure. In addition, the study sought to replicate the known effect of defocus on CS for the OKN-based measurements in emmetropic participants.MethodsFifteen participants viewed a horizontally moving grating while their eyes were tracked with an infra-red (IR) eye-tracker. To simulate the clinical conditions of the CS measurements, the participants were stimulated monocularly as the left eye was occluded by an IR filter. The horizontal eye position was continuously analyzed for OKN responses, and the stimulus contrast was changed by an adaptive psychometric method depending on the outcome. Furthermore, the newly proposed OKN live-detection was verified against an offline analysis and an expert-observer judgement. The OKN-based CS was measured for six spatial frequencies at normal vision and three levels of defocus using spherical convex lenses.ResultsThe newly proposed OKN live-detection method showed a sufficient detection performance for implementation of adaptive procedures, and the detection rate is similar or better compared to offline detection methods. Spatial frequency and defocus had a significant effect on the OKN-based CS (P < 0.0001 for both).ConclusionsThe current study presents a novel method to measure motion CS in an automated way, combining the real-time detection of OKN and an adaptive psychometric procedure. Furthermore, the known effect of defocus on CS was successfully replicated with the newly developed tool.Translational RelevanceOKN-based CS is a novel approach to assess spatial vision, which is sensitive to subtle effects of defocus, allowing use with nonverbal patients and infants. Furthermore, the newly developed tool may improve the performance of such measurements.

Differential Involvement of EEG Oscillatory Components in Sameness versus Spatial-Relation Visual Reasoning Tasks.

The development of deep convolutional neural networks (CNNs) has recently led to great successes in computer vision, and CNNs have become de facto computational models of vision. However, a growing body of work suggests that they exhibit critical limitations on tasks beyond image categorization. Here, we study one such fundamental limitation, concerning the judgment of whether two simultaneously presented items are the same or different (SD) compared with a baseline assessment of their spatial relationship (SR). In both human subjects and artificial neural networks, we test the prediction that SD tasks recruit additional cortical mechanisms which underlie critical aspects of visual cognition that are not explained by current computational models. We thus recorded electroencephalography (EEG) signals from human participants engaged in the same tasks as the computational models. Importantly, in humans the two tasks were matched in terms of difficulty by an adaptive psychometric procedure; yet, on top of a modulation of evoked potentials (EPs), our results revealed higher activity in the low β (16–24 Hz) band in the SD compared with the SR conditions. We surmise that these oscillations reflect the crucial involvement of additional mechanisms, such as working memory and attention, which are missing in current feed-forward CNNs.

Effects of ear-canal static pressure on pure-tone thresholds and wideband acoustic immittance.

Wideband acoustic immittance (WAI) measures provide information about middle-ear function across the traditional audiometric frequency range from 0.25 to 8.0 kHz. Recent studies have found that WAI is effective in predicting the presence of conductive hearing loss (CHL). It is not known whether WAI can accurately estimate the degree of threshold shift caused by CHL. The purpose of the present study was to evaluate the relationship between changes in pure-tone threshold and changes in wideband absorbance and acoustic conductance levels induced by positive and negative ear-canal static pressure. Twenty young adult subjects with normal hearing and a negative history of middle-ear disorders participated in the study. Experimental pure-tone thresholds at 0.5 and 2.0 kHz were estimated by using a three-interval, three-alternative forced-choice adaptive psychometric procedure under three conditions: ambient ear-canal pressure, +200 daPa static pressure, and -200 daPa static pressure. Wideband absorbance and conductance were obtained in the same subjects by using a Welch Allyn prototype diagnostic middle ear analyzer. Changes in pure-tone threshold from the ambient pressure condition to the static pressure condition were evaluated by using a paired-samples t test and Pearson product-moment correlation. Wideband middle-ear absorbance and conductance at ambient pressure in this study were consistent with published data in adults with normal hearing. The mean change in threshold at 0.5 and 2.0 kHz with +200 daPa or -200 daPa ear-canal static pressure was similar to the mean change in absorbance and conductance levels in the same conditions. However, there was one statistically significant difference between the shift in pure-tone threshold and the change in conductance level for the +200 daPa pressure condition for 2.0 kHz, with the change in threshold being 1.5 dB greater than the change in conductance level (t = 2.39, p = 0.03). In contrast to the good performance of WAI measures in predicting mean threshold shifts caused by ear-canal pressure, the shifts in WAI were not correlated with threshold shifts. Thus WAI was not well suited to predict individual threshold changes caused by ear-canal static pressure. For the conditions of this study, results suggest that mean change in absorbance or conductance level caused by ear-canal static pressure of +200 daPa or -200 daPa provides a good estimate of the change in pure-tone threshold in the same conditions. However, individual threshold change was not accurately predicted by the change in absorbance or conductance level.

Evaluation of Single Pixel Step Sizes in Visual Acuity Assessment

Adaptive thresholding procedures (e.g., ZEST) benefit from testing near the current estimate of threshold. Therefore, small increments may improve precision of these techniques. We evaluated the validity of visual acuity assessment when letters are not constrained to a multiple of 5 pixels high. Snellen letters were presented over a ±5 pixel range spanning the final threshold estimate. Sizes that were a multiple of 5 pixels (e.g., 20 and 25) were presented 160 times, and other sizes were presented 40 times. This resulted in 320 letter presentations at multiples of 5 and at non-multiples of 5. Post hoc ZEST procedures were used to compute acuity threshold estimates based on testing at those two sets of sizes. Two subjects participated: subject 1 for the right and left eyes and subject 2 in two sessions with binocular viewing. Psychometric functions were fit to the data and were used to model simulated observers. Simulations were run for each data set, and the number of presentations at each size matched the number presented to the subject. Ninety percent limits for proportion correct at each letter size were determined from the simulation data, and these limits were used as criteria for identifying outliers in the subject's data. No significant difference in acuity thresholds were found when letters were rendered in multiples of 5 pixel heights vs. letters without this constraint. Empirical data fell within the bounds defined by simulations, with no idiosyncratic results found for either set of letter sizes. Letter sizes that do not conform to a multiple of 5 pixel letter height yield valid acuity scores. This facilitates adaptive psychometric procedures for acuity testing, such as ZEST and QUEST, in which letter sizes are selected to be as close to the current estimate of threshold size as possible.

Comparison of adaptive psychometric procedures motivated by the Theory of Optimal Experiments: Simulated and experimental results

The wide use of psychometric assessments and the time necessary to conduct comprehensive psychometric tests has motivated significant research into the development of psychometric testing procedures that will provide accurate and efficient estimates of the parameters of interest. One potential framework for developing adaptive psychometric procedures is the Theory of Optimal Experiments. The Theory of Optimal Experiments provides several metrics for determining informative stimulus values based on a model of the psychometric function to be provided by the investigator. In this study, two methods based on a previous implementation of the Theory of Optimal Experiments are presented for comparison to two fixed step size staircase methods and also an existing adaptive method that utilizes a Bayesian framework. The psychometric procedures were used to measure detection thresholds and discrimination limens on two separate psychoacoustic tasks with normal-hearing subjects. Computer simulations were performed based on the outcomes of the experimental psychoacoustic detection task to analyze performance over a large sample size in the case of known truth. Results suggest that the proposed stimulus selection rules motivated by the Theory of Optimal Experiments perform better than previous techniques and also extend estimation to multiple parameters.

A comparison of adaptive psychometric procedures based on the theory of optimal experiments and Bayesian techniques: Implications for cochlear implant testing

Numerous previous studies have focused on the development of quick and efficient adaptive psychometric procedures. In psychophysics, there is often a model of the psychometric function supported by previous studies for the task of interest. The theory of optimal experiments provides a framework for utilizing a model of the process to develop quick and efficient sequential-testing strategies for estimating model parameters, making it appropriate for developing adaptive psychophysical-testing methods. In this study, we investigated the application of sequential parameter search strategies based on the theory of optimal experiments and Bayesian adaptive procedures for measuring psychophysical variables. The results presented in this article suggest that more sophisticated psychometric procedures can expedite the measurement of psychophysical variables. Such techniques for quickly collecting psychophysical data may be particularly useful in cochlear implant research, where a large set of psychophysical variables are useful for characterizing the performance of an implanted device. It is to be hoped that further development of these techniques will make psychophysical measurements available to clinicians for tuning and optimizing the speech processors of individual cochlear implant patients.

Sensitivity analysis to evaluate the benefits and risks of using prior information in adaptive psychometric procedures

Numerous adaptive psychometric procedures have been developed based on a Bayesian framework. In these procedures, a key component for estimating the targeted parameter and determining the next stimulus value is the parameter probability distribution. The presence of a parameter probability distribution introduces the opportunity to include prior information via initialization of the parameter probabilities. However, differences in the techniques for parameter estimation and stimulus selection may determine how various psychometric procedures benefit from accurate prior information or recover from inaccurate prior information. In this study, several adaptive psychometric procedures using a Bayesian framework were investigated through simulation of a psychophysical task. The simulations included prior information with varying degrees of accuracy and varying levels of initial confidence. Results suggest that the benefits of prior information are dependent on the specific psychometric procedure and the inclusion of prior information may influence the final choice of an appropriate psychometric procedure.

Maximum-likelihood psychometric procedures in two-alternative forced-choice: evaluation and recommendations.

Several new adaptive psychometric procedures have been proposed that use maximum-likelihood methods to estimate points on a subject’s psychophysical function. These developments are summarized, and some psychometric situations that pose special problems for the new approaches are examined. The problem areas include the effects of threshold changes during the testing session, the impact of errors made by the subject, and differences between yes-no and two-alternative forced-choice situations. Data are presented from both human subjects and computer simulations. Strengths and weaknesses of the new procedures are identified and recommendations are made for their use.

QUEST: a Bayesian adaptive psychometric method.

An adaptive psychometric procedure that places each trial at the current most probable Bayesian estimate of threshold is described. The procedure takes advantage of the common finding that the human psychometric function is invariant in form when expressed as a function of log intensity. The procedure is simple, fast, and efficient, and may be easily implemented on any computer.