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Biomedical subjects

T E Hanna

Publications and source records attributed to T E Hanna.

15 recordsLinked to original sources
PubMed1992

Human efficiency for visual detection of targets on cathode ray tube displays using a two-level multiple-channel time history format.

Human observers were tested for their ability to detect targets on visual displays. The displays simulated the multiple-channel time history format, using two levels of intensity encoding. A target was presented on 50% of the trials at a constant bearing. Observers indicated their judgment as to whether a target was present by using a four-category rating scale. Receiver-operating characteristics (ROCs) were generated from the rating data and compared to ROCs for an optimal detector. In experiment I, data were collected for two signal-to-noise ratios and for 32, 64, and 128 lines of data. Results indicated that observers were 3-5 dB less sensitive than an optimal detector. Performance improved as the number of lines increased but not to the extent predicted by optimal integration of information across lines of the display. In experiment II, the bearing at which subjects judged whether a target was present, was clearly delineated from the background by encoding information presented at this bearing in red. The purpose of experiment II was to determine the degree to which human inefficiency in detecting targets is due to the inability to focus on a single column of data. Subject performance improved when the red encoding was utilized, but subjects still performed 2 dB below ideal. This suggests that subjects use a suboptimal decision rule for judging the presence of the target.

Attention↗
PubMed1992

Discrimination and identification of modulation rate using a noise carrier.

Modulation-rate perception was measured for three tasks: a fixed-standard, forced-choice discrimination task with a 500-ms interstimulus interval; a random-standard, forced-choice discrimination task with an 8-s interstimulus interval; and an identification task. Thresholds were obtained for modulation rates from 14-224 Hz using noise carriers bandpass filtered from 500-4000 Hz, 500-1600 Hz, 1700-2800 Hz, and 2900-4000 Hz. The four bands yielded similar results except for modulation rates greater than 100 Hz, where the 500- to 1600-Hz thresholds were higher. Fixed-standard discrimination thresholds were about 3 Hz for modulation rates up to 66 Hz. The increase of thresholds for modulation rates above 66 Hz could be due to temporal resolution limits with a time constant of about 2-3 ms. For modulation rates above 100 Hz, critical-band filtering may further decrease sensitivity for the 500- to 1600-Hz noise band. Resolution in the random-standard discrimination task was similar to that for the identification task. Thresholds were elevated relative to fixed-standard thresholds except at the extremes of the stimulus range. In the random-standard discrimination task, a pronounced criterion bias was present for stimuli near the extremes of the range. Durlach and Braida's model [N. I. Durlach and L. D. Braida, J. Acoust. Soc. Am. 46, 372-383 (1969)] describes the data well and provides quantitative measures for our data in good agreement with those for intensity perception.

Adult↗
PubMed1992

Masking in three-dimensional auditory displays.

The extent to which simultaneous inputs in a three-dimensional (3D) auditory display mask one another was studied in a simulated sonar task. The minimum signal-to-noise ratio (SNR) required to detect an amplitude-modulated 500-Hz tone in a background of broadband noise was measured using a loudspeaker array in a free field. Three aspects of the 3D array were varied: angular separation of the sources, degree of correlation of the background noises, and listener head movement. Masking was substantially reduced when the sources were uncorrelated. The SNR needed for detection decreased with source separation, and the rate of decrease was significantly greater with uncorrelated sources than with partially or fully correlated sources. Head movement had no effect on the SNR required for detection. Implications for the design and application of 3D auditory displays are discussed.

Adolescent↗
PubMed1992

Estimation of psychometric functions from adaptive tracking procedures.

Because adaptive tracking procedures are designed to avoid stimulus levels far from a target threshold value, the psychometric function constructed from the trial-by-trial data in the track may be accurate near the target level but a poor reflection of performance at levels far removed from the target. A series of computer simulations was undertaken to assess the reliability and accuracy of psychometric functions generated from data collected in up-down adaptive tracking procedures. Estimates of psychometric function slopes were obtained from trial-by-trial data in simulated adaptive tracks and compared with the true characteristics of the functions used to generate the tracks. Simulations were carried out for three psychophysical procedures and two target performance levels, with tracks generated by psychometric functions with three different slopes. The functions reconstructed from the tracking data were, for the most part, accurate reflections of the true generating functions when at least 200 trials were included in the tracks. However, for 50- and 100-trial tracks, slope estimates were biased high for all simulated experimental conditions. Correction factors for slope estimates from these tracks are presented. There was no difference in the accuracy and reliability of slope estimation due to target level for the adaptive track, and only minor differences due to psychophysical procedure. It is recommended that, if both threshold and slope of psychometric functions are to be estimated from the trial-by-trial tracking data, at least 100 trials should be included in the tracks, and a three- or four-alternative forced-choice procedure should be used. However, good estimates can also be obtained using the two-alternative forced-choice procedure or less than 100 trials if appropriate corrections for bias are applied.

Attention↗
PubMed1991

An interleaved tracking procedure to monitor unstable psychometric functions.

In some experimental situations, the psychometric function underlying performance may not be stable, but instead may shift along the stimulus axis in response to changes in attention, learning, or task difficulty. When this occurs, the measured threshold may be influenced and the slope of the measured function will be inaccurately shallow. With commonly used experimental procedures, it is difficult to know whether a shallow psychometric function slope is a true reflection of the sensory process, or is a result of "averaging" a highly variable underlying function. Here, a new method is described of estimating psychometric function slope from the variability in two interleaved adaptive tracks, consulted on alternate trials, that is resistant to the effects of shifting performance levels. Further, a mechanism is described for assessing the likelihood that a threshold was, in fact, stable over the course of its measurement. Computer simulations are reported as well as verification of the method in measurements of human performance on a psychophysical task. Several conditions of externally imposed variability were simulated to establish the ability of these procedures to identify unstable functions and produce accurate slope estimates. The procedures worked well for thresholds shifting by as little as 4 dB if the variation did not occur too rapidly. The procedure and associated analyses are recommended as a relatively "free" means of calculating slope and quantifying threshold reliability with little extra experimental effort.

Attention↗
PubMed1989

Evaluation of stopping rules for audiological ascending test procedures using computer simulations.

Stopping rules for ascending audiological test procedures were evaluated by Monte Carlo simulation. The stopping rules differed in the minimum number of responses required at a level, whether these responses occurred on half or a majority of the ascending series, and whether all or only the most recent ascending series were considered. For all procedures, shallow psychometric function slopes yielded estimated thresholds closer to the level giving 50% detection than did steeper slopes, which yielded estimated thresholds roughly 2.5 dB above the level corresponding to 50% on the psychometric function. Shallow slopes also resulted in decreased reliability across threshold measurements, an increased number of trials required for threshold estimates, and a higher proportion of measurements that had to be repeated. Stopping rules using a two-response criterion were faster than those using a three-response criterion, with only a small decrease in reliability. Among stopping rules using the same number of responses for criterion, differences were seen primarily in efficiency for shallow slopes, particularly for procedures using a three-response rather than a two-response criterion for stopping. Results from these simulations should be useful to standards groups.

Audiometry↗
PubMed1989

Enhanced detection with bimodal sonar displays.

Signal-to-noise ratios (SNRs) required to detect narrow-band signals in white noise were compared for bimodal and single-modality sonar displays at two levels of signal uncertainty and two degrees of spatial compatibility between the auditory and visual displays. In bimodal test conditions the auditory and visual signals were equated in detectability for each subject. An adaptive, two-alternative, forced-choice procedure was used to maintain a constant percentage of correct responses. The decrement in performance with increased signal uncertainty was significantly greater for visual than for auditory displays, suggesting that auditory displays offer advantages for real-world sonar operations. Bimodal displays produced a reliable advantage in SNR required for detection over single-modality displays. Increased compatibility between the visual and auditory displays did not increase the advantage of bimodal presentation, nor did increased signal uncertainty. It was concluded that bimodal displays enhance operators' perceptual sensitivity. The magnitude of the enhancement was consistent with optimal integration of information in the two modalities.

Adult↗
PubMed1988

Evidence for sensory-trace comparisons in spectral shape discrimination.

The ability of experienced observers to discriminate changes in the shapes of complex sound spectra was studied for three conditions. In one condition, the reference spectrum or "background" was fixed in spectral shape across each block of trials; in a second condition, the reference spectrum differed in spectral shape from trial to trial within each block of trials but was the same for the two presentations within a trial; and, in a third condition, the reference spectrum differed in spectral shape on every stimulus presentation. The variation in the reference spectrum was a random perturbation in the amplitudes of the tonal components comprising the complex sounds. The signal was an intensity increment to the center component (1000 Hz) of the complex and was present in one interval of each two-interval, two-alternative, forced-choice trial. The principal experimental manipulations were the degree of amplitude perturbation of the reference spectrum and the interval of time between the two stimulus presentations of each trial (interstimulus interval, ISI). The theory proposed by Durlach and Braida [J. Acoust. Soc. Am. 46, 372-383 (1969)] describing memory processes involved in the perception of sound intensity was used to explain the experimental results. As that theory was applied in this study, only the condition in which the stimuli were perturbed between trials showed evidence for comparisons based on "sensory traces," while the conditions in which the stimuli were fixed or were perturbed within trials were best explained by comparisons based on judgments relative to the stimulus context.

Acoustic Stimulation↗
PubMed1986

Absolute intensity discrimination using two responses.

The observer was asked to judge whether a comparison sound was more or less intense than a standard sound of 60 dB SPL. The sounds were broadband noises of 100-ms duration. The independent variables were the range of intensities used in the set of comparison sounds and the presence or absence of feedback. The main dependent variable was the variability of such judgments, which was measured from the psychometric function. The variability, measured in terms of the Weber function, increased from about 1.5 to 4 dB when the stimulus range changed from 10 to 60 dB. Increases in stimulus range increased the variability of the binary judgments in this task, as they had in previous experiments where multiple responses were required. Feedback improved performance primarily at the largest ranges. Only a small fraction of these changes in variability stems from sequential effects.

Acoustic Stimulation↗
PubMed1986

Effect of signal phase and masker separation on two-tone masking.

The detectability of a sinusoid masked by two sinusoids was studied as a function of signal phase and the frequency separation between the two maskers. The signal frequency fs was equal to the arithmetic mean of the two masker frequencies, fl and fh, where fl less than fh. Signal frequencies of 1 and 4 kHz, eight signal phases, and 12 values of r = (fh-fl)/fs from 0.01-1.0 were used. The data could be divided into three regions. For large masker separations, r greater than 0.4, no consistent effects of signal phase were observed. For r less than 0.4, an effect of signal phase was evident at both signal frequencies. However, the effect of signal phase was different for the two regions 0.03 less than r less than 0.4 and r less than 0.03. For moderate masker separations, 0.03 less than r less than 0.4, masked thresholds were lowest at phases of 0 degrees and 180 degrees and highest at phases of 90 degrees and 270 degrees. For small masker separations, r less than 0.03, masked threshold was highest at 0 degree and the effect of signal phase depended on signal frequency. The different form of the phase effect for these three regions is discussed in terms of the use of different cues, arising from temporal resolution, spectral filtering, combination tones, and envelope spectra.

Auditory Threshold↗
PubMed1986

Detection and intensity discrimination of a sinusoid.

Intensity discrimination thresholds were measured for gated 100-ms, 1000-Hz tones. Discrimination thresholds were measured at several intensities near absolute threshold as well as at 30, 60, and 90 dB SPL. Psychometric functions were obtained for several of these discrimination conditions, and for detection of the signal in quiet. The results showed that Weber's law is approximately valid for standards as low as 0 dB SL. Small amounts of negative masking were observed even when the data were expressed in terms of increment energy. The psychometric functions for the discrimination conditions had a similar form and were shallower than the psychometric function for the detection of a signal in quiet. A similar set of conditions was run in the presence of a continuous, broadband noise. The results were generally in agreement with those obtained in quiet, but slight differences suggested that the variability which limits performance in the two conditions is different. The results are discussed in terms of the effects of nonlinear transduction, the effects of uncertainty, and contrast mechanisms as proposed by Laming [Sensory Analysis (Academic, London, 1986)].

Adolescent↗
PubMed1985

Effects of masker waveform and signal-to-masker phase relation on diotic and dichotic masking by reproducible noise.

The proportions of hits and false alarms were estimated for the detection of a 500-Hz sinusoidal signal in each of 25, reproducible samples of wideband, white, Gaussian noise. The effects of signal phase were investigated under diotic (MoSo) and dichotic (MoS pi) conditions and compared to the predictions of two major models of binaural hearing. Averaging the data over samples obscured important across-sample and across-subject differences in performance. The proportions of hits and false alarms for individual noise samples presented under the MoSo condition were highly correlated with those for the same noise samples under the dichotic MoS pi condition, suggesting that the cues determining performance under these conditions are related. Signal-to-masker phase had a large effect on the proportion of hits under the MoSo condition, but only a small effect under the MoS pi condition. The Vector model predicts a large effect of signal phase under the MoS pi condition, and is, therefore, imcompatible with this aspect of the data. The expected value of the decision variable of the EC model is independent of signal phase. However, when the variance of the decision variable is also considered, the EC model does predict changes in the proportion of hits with the phase of the signal, comparable to those observed here. Further, it was shown that, if minor changes in the form of the EC model's decision variable or in the distribution of the internal noise parameters are assumed, the expected value of the decision variable also changes with the phase of the signal.

Acoustic Stimulation↗
PubMed1984

Profile analysis and level variation.

This study examines the effects of random level variation, a method used in studies of profile analysis [3-6,14,15]. Presentation levels for a complex of sinusoids are varied randomly on each interval of a two-interval, forced-choice detection task in which subjects are required to detect an increment on one of the sinusoidal components of the complex. Three experiments are reported. The first experiment examines the effect of the range of level variation. The second is concerned with the effects of the median level about which the presentation levels vary. The third experiment is designed to provide a within-trial analysis of the effect of the differences in presentation levels. As the range of level variation is increased, ability to detect the increment decreases. The results indicate that detection performance is best at moderate intensity levels and decreases at lower and higher levels. Finally, the difference in levels within a single trial has little if any effect.

Acoustic Stimulation↗
PubMed1982

Forward masking of diotic and dichotic clicks by noise.

The first experiment reported here measured thresholds for clicks in forward masking as a function of the masker level and as a function of the temporal relation of a 6-kHz low-pass noise masker to the click (300-msec duration with a 20-msec temporal gap or 10-msec duration with a 5-msec gap). Also varied were the spectral content of the click (low-pass filtered at 1 or 5 kHz) and the interaural phase of the click (0 or pi). The difference in frequency content had no effect on the amount of masking for the 300-msec masker, while with the 10-msec masker greater masking was found for the 1-kHz click. This combination (1 kHz, 10 msec) was also the only one to produce Masking Level Differences (MLDs) when the click was presented dichotically. A second experiment investigated the effects of combining the maskers used in the first experiment. Additional masking (above that predicted by an energy sum) was found, as has been reported elsewhere [Penner and Shiffrin, A. Acoust. Soc. Am. 67, 617-627 (1980)]. However, the magnitude of this additional masking was decreased for certain conditions. These data conflict with the predictions of additivity of masking obtained from a model proposed by Penner and Shiffrin and suggest that modifications to that model are needed. The results of both experiments can be explained by assuming that two processes are acting in forward masking [Duifhuis, J. Acoust. Soc. Am. 54, 1471-1488 (1973)].

Acoustic Stimulation↗