Barbara Anne Dosher

Strategies for multiattribute binary choice.

Based on eye-fixation patterns, strategies for multiattribute binary choice were classified as holistic (within an alternative) or dimensional (within an attribute across alternatives). In a task environment hospitable to both strategies, dimensional processing predominated. Even for alternatives like simple gambles, which require holistic computations, dimensional strategies were used as often as holistic ones. The dimensional strategies were augmented by two procedures that simplify the computations. These simplification procedures reduce cognitive effort at the cost of a relatively small increase in errors. However, for about half the subjects the use of these simplification procedures led to systematic violations of expected utility theory on certain choices. Both the preference for dimensional over holistic strategies and the adoption of simplifying procedures are compatible with the desire to reduce cognitive effort. We propose that strategies are selected to minimize the joint cost of errors and effort.

Mechanisms of Perceptual Learning

What is learned in perceptual learning? How does perceptual learning change the perceptual system? We investigate these questions using a systems analysis of the perceptual system during the course of perceptual learning using psychophysical methods and models of the observer. Effects of perceptual learning on an observers performance are characterized by external noise tests within the framework of noisy observer models. We find evidence that two independent mechanisms, external noise exclusion and stimulus enhancement support perceptual learning across a range of tasks. We suggest that both mechanisms may reflect re-weighting of stable early sensory representations.

Noise Exclusion in Spatial Attention

Precue validity affects the performance of perceptual tasks. These spatial attention effects have been variously attributed to facilitation of processing, capacity allocation, or noise reduction. We used a new attention-plus-external (stimulus)-noise paradigm and model to identify the mechanisms of attention in cue-validity paradigms. A new phenomenon is reported: a large effect of location cue validity in an orientation identification task that specifically occurs when the stimulus is embedded in external (environmental or stimulus) noise. This result identifies the mechanism of the effect as external-noise exclusion, distinguished from stimulus enhancement that manifests itself only in noiseless stimulus environments.

Task precision at transfer determines specificity of perceptual learning.

Perceptual learning, the improvement in performance with practice, reflects plasticity in the adult visual system. We challenge a standard claim that specificity of perceptual learning depends on task difficulty during training, instead showing that specificity, or conversely transfer, is primarily controlled by the precision demands (i.e., orientation difference) of the transfer task. Thus, for an orientation discrimination task, transfer of performance improvement is observed in low-precision transfer tasks, while specificity of performance improvement is observed in high-precision transfer tasks, regardless of the precision of initial training. The nature of specificity places important constraints on mechanisms of transfer in visual learning. These results contribute to understanding generalization of practiced improvements that may be key to the development of expertise and for applications in remediation.

Tradeoffs between stereopsis and proximity luminance covariance as determinants of perceived 3D structure

A 2D polar projection of a 3D wire cube (Necker cube) in clockwise rotation can be perceived either veridically as a clockwise-rotating cube (rigid percept) or as a counterclockwise-rotating rubbery, truncated pyramid (nonrigid percept). The 3D percept is influenced by various cues: linear perspective, stereo disparity, and proximity-luminance covariance (PLC, the intensification of edges in proportion to their proximity to the observer). Perspective, by itself or in combination, is a very weak cue whereas PLC is a powerful cue [Schwartz and Sperling (1983) Bull. Psychon. Soc. 21, 456-458]. Here we determined psychometric functions for perceptual resolution in static displays and dynamic rotating displays (with and without a static preview) as determined by stereopsis and PLC in isolation and with both cues jointly, possibly in conflict. Stereopsis was the dominant cue in static displays and in most dynamic displays. When a static display preceded a dynamic display, it strongly influenced the subsequent dynamic percept. Perceptual resolution in all conditions was accurately described by a winner-take-all model in which the strength of evidence for each percept from different cues is simply algebraically added.

Mechanisms of perceptual attention in precuing of location

What are the mechanisms of spatial attention underlying precue validity effects? We answer this question within the framework of a perceptual template model (PTM) [Lu & Dosher (1998). External noise distinguishes attention mechanisms. Vision Research, 38, 1183-1198; Dosher & Lu (1999). Mechanisms of perceptual learning. Vision Research, 39, 3197-3221] and an external noise plus attention paradigm for orientation judgments in two- to eight-location displays. Attentional mechanisms correspond to behavioral signatures: External noise exclusion produces cuing effects in high external noise and stimulus enhancement produces cuing effects in noiseless displays. We found that external noise exclusion was the primary mechanism of cue validity effects, with large effects in high-noise displays. Stimulus enhancement coexisted as a secondary mechanism in noiseless displays for a subset of observers and display conditions. Contrast threshold ratio tests ruled out attentionally mediated changes in gain control. The ratio rules were also shown to hold for a stochastic PTM model. Effects were equivalent for four-alternative (Experiment 1) and two-alternative (Experiment 2) orientation identification. Precues allow observers to reduce noise and focus on the target in the precued location. External noise exclusion was more important in larger displays. Previous results are reclassified and understood within the PTM framework.

Spatial Attention: Different Mechanisms for Central and Peripheral Temporal Precues?

The external noise paradigm (Z.-L. Lu & B. A. Dosher, 1998) was applied to investigate mechanisms of spatial attention in location precuing. Observers were precued or simultaneously cued to identify 1 of 4 pseudocharacters embedded in various amounts of external noise. The cues were either central or peripheral. Both central and peripheral precuing significantly reduced threshold in the presence of high external noise (16% and 17.5%). Only peripheral precuing significantly reduced threshold in the presence of low, or no, external noise (11%). A perceptual template model identified different mechanisms of attention for central and peripheral precuing, external noise exclusion for central precuing, and a combination of external noise exclusion and stimulus enhancement (or equivalently, internal additive noise reduction) for peripheral cuing.

Characterizing Observers Using External Noise and Observer Models: Assessing Internal Representations With External Noise

External noise methods and observer models have been widely used to characterize the intrinsic perceptual limitations of human observers and changes of the perceptual limitations associated with cognitive, developmental, and disease processes by highlighting the variance of internal representations. The authors conducted a comprehensive review of the 5 most prominent observer models through the development of a common formalism. They derived new predictions of the models for a common set of behavioral tests that were compared with the data in the literature and a new experiment. The comparison between the model predictions and the empirical data resulted in very strong constraints on the observer models. The perceptual template model provided the best account of all the empirical data in the visual domain. The choice of the observer model has significant implications for the interpretation of data from other external noise paradigms, as well as studies using external noise to assay changes of perceptual limitations associated with observer states. The empirical and theoretical development suggests possible parallel developments in other sensory modalities and studies of high-level cognitive processes.

Serial retrieval processes in the recovery of order information

The retrieval of temporal order and item information from short-term memory (STM) are examined with the cued-response speed-accuracy trade-off (CR-SAT) procedure and a complementary reaction time (RT) task. The retrieval of order information was examined with a two-alternative forced-choice (2AFC), relative judgment of recency (JOR) task. Analyses of the pattern of mean RT, RT accuracy, and the overall shape of the RT distribution for correct JORs suggest that order information is retrieved by a serial retrieval mechanism. Analyses of SAT retrieval functions confirm that order information is retrieved by a recency-based, serial retrieval process. These results contrast with previous SAT analyses of STM item recognition (B. McElree & B. A. Dosher, 1989), which indicate that item information is retrieved by a parallel or direct-access mechanism. The dissociation between item and order information retrieval was further documented in a 2AFC item recognition SAT study

Discriminating preexperimental (semantic) from learned (episodic) associations: A speed-accuracy study ☆

This research investigates the process by which people discriminate preexperimental (semantic) from experimental (episodic) associations. Subjects were instructed to recognize (reply old) only to experimentally studied materials. The questions are how is context information used to select relevant memories, and how successful is the exclusion of irrelevant information? The recognition accuracy and the retrieval speed (rate of approach to asymptotic accuracy) are jointly measured using a speed-accuracy trade-off (SAT) paradigm, with collateral reaction time (RT) experiments. Experiment 1 presented both semantically related and unrelated pairs for study. In Experiment 3, semantically related pairs were never presented for study and preexperimentally related lures could be rejected by rule. Semantically related lures in both of these SAT experiments showed evidence for elevated false alarm rates early in retrieval, followed by late suppression of false alarms (at about 1 s). When related pairs were studied in the experiment, suppression was incomplete; when related pairs were never studied, rule-based supersuppression obtained. Results from collateral reaction time studies (Experiments 2 and 4) showed points that corresponded to the pattern of results in Experiments 1 and 3 near asymptote, although the RT data by themselves would have been interpreted quite differently. These results are compatible with a single-store, two-phase retrieval model in which context information, or recall-like information about correct pair mates, is used to correct spurious false alarms resulting from the incomplete filtering of semantic information.