Measurement of low-signal suppression and other parameters of the forced-choice psychometric function

Empirical forced-choice psychometric functions often depart in shape from those based on the theory of normal sensory-excitation distributions and optimal decision processes. The typical departure is that the detectability of small signals is too low compared to that of high signals. Some possible explanations were reviewed and it was emphasized that the source of the effect is not known with certainty. An extra parameter resembling a threshold was introduced for the measurement of the effect, and a method of moments was proposed for estimating the two parameters of the resulting two-alternative forced-choice psychometric function. The method was tried out with success in the task of detecting a 0.1-sec luminance increment to a steady adapting luminance of a large visual target. There were large amounts of low-signal suppression, indicating the advisability of reviewing some current psychophysical practices.     

The time course of gaze bias in visual decision tasks

In three experiments, we used eyetracking to investigate the time course of biases in looking behaviour during visual decision making. Our study replicated and extended prior research by Shimojo, Simion, Shimojo, and Scheier (2003), and Simion and Shimojo (2006). Three groups of participants performed forced-choice decisions in a two-alternative free-viewing condition (Experiment 1a), a two-alternative gaze-contingent window condition (Experiment 1b), and an eight-alternative free-viewing condition (Experiment 1c). Participants viewed photographic art images and were instructed to select the one that they preferred (preference task), or the one that they judged to be photographed most recently (recency task). Across experiments and tasks, we demonstrated robust bias towards the chosen item in either gaze duration, gaze frequency or both. The present gaze bias effect was less task specific than those reported previously. Importantly, in the eight-alternative condition we demonstrated a very early gaze bias effect, which rules out a postdecision response-related explanation.     

Vibrotactile masking: A comparison of psychophysical procedures

The amounts of ipsilateral and contralateral masking obtained with a modified psychophysical procedure were compared for vibratory stimuli presented to different body loci. Results of a combined forced-choice localization task and a forced-choice detection task were similar to the results obtained in previous investigations which employed method of limits and two-alternative, temporal forced-choice procedures, respectively. Ipsilateral maskers produced similar amounts of masking in both the detection and localization tasks for fingertip and arm test sites. Contralateral maskers resulted in considerably more masking in the localization task than in the detection task for both fingertip and arm test sites. When large longitudinal distances were introduced between the test stimulus and masker, little masking was evident in either the localization or detection task. It was concluded that the differences in the amount of ipsilateral and contralateral masking obtained with different psychophysical procedures reflect different effects of a masker on the detectable attributes of a test stimulus. Implications of these results for the study of multiple tactile perception were discussed.     

Comparison among four psychophysical procedures used in lateralization

Psychometrie functions were obtained from two listeners in four psychophysical tasks. The tasks were lateralization procedures in which Os were asked to make discriminations of interaural temporal differences of a 250-Hz tone. The four tasks were: a single-interval yes-no task, a single-interval left-right task, a two-alternative forced-choice task, and a two-interval same-different task. The theory of signal detection provides predictions relating the performances obtained in these four procedures. These predictions could not be verified in this experiment when it was assumed that the Os were listening to changes in lateral position produced by the interaural temporal difference. The data were, however, consistent with the assumption that Os use lateral motion as a cue for detection in two-interval tasks and lateral position as a cue in single-interval tasks.     

Guessing Strategies, Aging, and Bias Effects in Perceptual Identification

In the typical single-stimulus perceptual identification task, accuracy is improved by prior study of test words, a repetition priming benefit. There is also a cost, inasmuch as previously studied words are likely to be produced (incorrectly) as responses if the test word is orthographically similar but not identical to a studied word. In two-alternative forced-choice perceptual identification, a test word is flashed and followed by two alternatives, one of which is the correct response. When the two alternatives are orthographically similar, test words identical to previously studied items are identified more accurately than new words (a benefit) but tests words orthographically similar to studied words are identified less accurately than new words (a cost). Ratcliff and McKoon (in press) argue that these are bias effects that arise in the decision stage of word identification. We report five experiments that examined the alternative hypothesis that these bias effects arise from postperceptual guessing strategies. In single-stimulus perceptual identification, repetition priming benefits were equally great for young and older adults who claimed to use deliberate guessing strategies and those who did not (Experiment 1). In contrast, only groups of young and older people who claimed to deliberately guess studied words in a two-alternative forced-choice task (Experiments 2 and 5) showed reliable benefits and costs. Costs and benefits were abolished in the two-alternative forced-choice task when a very long study list was used, presumably because the increased retrieval burden made the use of deliberate guessing strategies less attractive (Experiment 3). Under conditions similar to those of Experiment 3, repetition priming was observed in single-stimulus perceptual identification (Experiment 4). These results are consistent with the view that costs and benefits in the forced-choice perceptual identification task arise from deliberate guessing strategies but that those in the single-stimulus task do not. The possibility that the observed relationship between strategy reports and priming effects reflects erroneous postexperimental assessments of strategies by participants is also considered.     

Target duration effects on iconic memory: the confounding role of changing stimulus dimensions

Observers' accuracy in detecting a narrow spatial gap between two brief, luminous rectangles presented successively was determined within a two-alternative, forced-choice procedure. This successive-field task requires iconic memory, because the information (rectangle position) in the two presentations must be combined for successful gap detection. On this task, the effect of varying the duration of the first rectangle was systematically investigated over several target luminance levels and for several ISI conditions between rectangles. At the long ISI conditions (100 and 300 ms), the effects of increasing stimulus duration was to improve performance. However, at the brief ISI condition (20 ms), increasing stimulus duration initially depressed task performance. It was found that, with practice, this initial performance drop largely disappeared, and the beneficial influence of increasing target duration was again obtained. These results are discussed in terms of (a) a proposed retinal locus for the iconic memory involved and (b), at a more general level, the potentially distracting role of changing stimulus dimensions on a task employing transient stimuli as in the present study.     

Shifts of the psychometric function: Distinguishing bias from perceptual effects

Morgan, Dillenburger, Raphael, and Solomon have shown that observers can use different response strategies when unsure of their answer, and, thus, they can voluntarily shift the location of the psychometric function estimated with the method of single stimuli (MSS; sometimes also referred to as the single-interval, two-alternative method). They wondered whether MSS could distinguish response bias from a true perceptual effect that would also shift the location of the psychometric function. We demonstrate theoretically that the inability to distinguish response bias from perceptual effects is an inherent shortcoming of MSS, although a three-response format including also an “undecided” response option may solve the problem under restrictive assumptions whose validity cannot be tested with MSS data. We also show that a proper two-alternative forced-choice (2AFC) task with the three-response format is free of all these problems so that bias and perceptual effects can easily be separated out. The use of a three-response 2AFC format is essential to eliminate a confound (response bias) in studies of perceptual effects and, hence, to eliminate a threat to the internal validity of research in this area.     

Visual detection of signals in the presence of continuous and pulsed backqrounds

The detectability of intensity increments in the presence of continuous and pulsed backgrounds was investigated using a two-alternative, temporal, forced-choice procedure. Differences were found in intensity-duration reciprocity relations, the form of the Weber function, and the shape of the psychometric function between continuous- and pulsed-detection conditions. In a second study, signals were added either to a steady background (simple detection) or to background plus pedestal (pedestal detection). Two unusual phenomena were noted, namely, “negative masking” and the “pedestal effect.” The interpretation of the results in terms of a simple, Poisson-detection model is discussed.     

A forced-choice adaptive procedure for measuring auditory thresholds in children

A modification of the two-down/one-up tracking procedure was used to estimate thresholds of audibility in 46 children (ages 3 to 6 years) and 10 adults. A two-alternative forced-choice version (26 children, 5 adults) of this method was successful in estimating thresholds of audibility in 5-year-olds, but not in 3- and 4-year-olds. A single-interval version of the procedure was successful in estimating thresholds of audibility for all the children. Measures from the children of between- and within-subjects variability, psychometric functions, and response bias all indicate that the procedure enables one to estimate thresholds that are in close agreement with those obtained from adults and with results of other investigators.     

The Piéron function in the threshold region

The Piéron function (Piéron, 1914, 1920, 1952) describes the decay of reaction time (RT) when the intensity of the stimulus is increased. It is generally demonstrated within a suprathreshold range of intensities. However, in some studies, for the lowest range of intensities, the exponent of the function is clearly greater than that for the upper ranges of intensities. Such an increase in the exponent for the lowest intensities is assumed to result from a combined effect of stimulus intensity and of stimulis uncertainty in detection. Our first experiment used luminance levels that covered all the scotopic range and a spatial two-alternative forced-choice task in which both accuracy and RT were measured. It demonstrated a drastic increase in the exponent in the Piéron function when the intensities reached the threshold region. Since the estimates of the threshold region may have been biased by the use of a much larger range of luminances, a second experiment was conducted using luminances that covered only the threshold region. This experiment confirmed the previous estimates for the threshold region.     

Reaction times reveal the contribution of the different receptor components in luminance perception

Piéron (1914, 1920, 1952) demonstrated that simple reaction time decays as a hyperbolic function of luminance. Similarities between cell latencies and reaction time (RT) to luminance suggest that this relationship may be determined by retinal processes. If the exponent of the Piéron function is specific to a given sensory modality, as assumed by some authors (e.g., Bonnet, 1992a, 1992b; Norwich, 1987), it should reflect receptor activities. Consequently, functions with different exponents should fit data for different luminance ranges. In a contrast-discrimination experiment, we investigated this question with a large range of luminance levels in a two-alternative spatial forced-choice task. The results of the experiment show that three functions with different exponents fit RT to the three luminance ranges (scotopic, mesopic, and photopic). The exponent decreases with increasing luminance. The findings indicate that the exponent and the asymptotic latency of the RT function reflect receptor activities of the visual system.     

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.     

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.     

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.     

Psychophysics of remembering: to bias or not to bias

Delayed matching to sample is typically a two-alternative forced-choice procedure with two sample stimuli. In this task the effects of varying the probability of reinforcers for correct choices and the resulting receiver operating characteristic are symmetrical. A version of the task where a sample is present on some trials and absent on others is analogous to a yes/no recognition task. We describe data from two experiments where an asymmetry in performance in the yes/no task could be attributed to a change in response bias with increasing retention-interval duration from a matching-law perspective, but not from a signal-detection perspective. Both approaches make explicit assumptions about response bias. The apparent inconsistency between the two approaches to the treatment of response bias is resolved in terms of a model proposed by K. G. White and J. T. Wixted (1999) which predicts asymmetrical matching-law functions and receiver operating characteristics without making any assumptions about response bias.     

Visual detection as a function of attentional demand and perceptual system error

Attentional demands were varied in a two-alternative, forced-choice detection experiment. A bar indicator designated the target form in one condition and occurred in random locations in a second condition. Exposure durations necessary for predetermined single-form display HRs were determined for each of eight Ss to measure performance at different levels of perceptual system error. Forms differed in only a single feature. Detection was superior when the bar indicator designated the target form, and differences increased with increased display size. Evidence for interference in detection due to the presence of nontarget forms apart from noting requirements of such forms was found. Estimates of number of perceptual channels noted did not clearly differentiate serial from parallel processing models. It was concluded that display interference error and spatial selectivity influences are important determinants of detection accuracy.     

Visual statistical learning produces implicit and explicit knowledge about temporal order information and scene chunks: Evidence from direct and indirect measures

We examined whether visual statistical learning (VSL) produced implicit and/or explicit knowledge about temporal order information and scene chunks, using a rapid serial visual presentation target detection task and a two-alternative forced-choice (2AFC) familiarity test as indirect and direct measures of VSL, respectively. In the familiarization phase, participants viewed a visual stream of natural scenes consisting of four triplets (i.e., three images that always appeared in the same order). In the subsequent target detection task, participants were required to detect target items embedded in a stream of 12 images or 12 words representing each natural scene. In the final 2AFC familiarity test, participants observed two test sequences (statistically related triplets vs. unrelated foils) and decided whether the first or second sequence was more familiar based on the familiarization phase. In both test phases, we included the same (forward) and reverse (backward) order of scenes as presented during the familiarization phase to examine whether the expression of VSL was based on temporal order of scenes or scene chunks. The results of the target detection task showed a learning effect for both temporal order in the forward condition and chunks in the backward condition, irrespective of whether stimuli were images or words; in contrast, we did not observe a learning effect in the backward condition for scene images in the familiarity test. Our findings are compatible with a learning mechanism that has both implicit and explicit components based on temporal order information and scene chunks.     

When are semantic targets detected faster than visual or acoustic ones?

Duration-discrimination data from an experiment using empty auditory intervals in a two-alternative forced-choice paradigm are presented. The observed functional relationship between standard deviation of the psychometric density function and stimulus duration is shown to be fit significantly better by a Weber’s law model of duration discrimination than by Creelman’s counter model. Both models fail to predict the rapid rise in the Weber fraction observed for durations longer than about 2 sec. However, the Weber’s law model, based on a generalization of Weber’s law, accurately predicts the initial drop in the Weber fraction for very short durations and the observed constancy of the Weber fraction for durations up to 2 sec.     

How task errors affect subsequent behavior: Evidence from distributional analyses of task-switching effects

Switch costs in task switching are often assumed to reflect the strengthening of task-related associations. Recently, we provided evidence that committing an error leads to the strengthening of the wrong task (Steinhauser & Hübner, 2006). In the present study, we report how error-induced control compensates for the effects of error strengthening. We hypothesized that, although error detection cannot prevent an error from being strengthened, it initiates processes that suppress the negative consequences of error strengthening on subsequent trials. Because error-induced control is known to operate slowly, we predicted that a compensatory effect should be observable only for slow responses. In three task-switching experiments, these predictions were confirmed by distributional analyses. The results extend our understanding of the interplay between procedural learning and executive control.     

Embodied Information in Cognitive Tasks: Haptic Weight Sensations Affect Task Performance and Processing Style

Research in the field of embodied cognition showed that incidental weight sensations influence peoples’ judgments about a variety of issues and objects. Most studies found that heaviness compared to lightness increases the perception of importance, seriousness, and potency. In two experiments, we broadened this scope by investigating the impact of weight sensations on cognitive performance. In Experiment 1, we found that the performance in an anagram task was reduced when participants held a heavy versus a light clipboard in their hands. Reduced performance was accompanied by an increase in the perceived effort. In Experiment 2, a heavy clipboard elicited a specific response heuristic in a two-alternative forced-choice task. Participants showed a significant right side bias when holding a heavy clipboard in their hands. After the task, participants in the heavy clipboard condition reported to be more frustrated than participants in the light clipboard condition. In both experiments, we did not find evidence for mediated effects that had been proposed by previous literature. Overall, the results indicate that weight effects go beyond judgment formation and highlight new avenues for future research.