A theory of criterion setting with an application to sequential dependencies.

Describes 3 models (the linear additive learning model, the exponential additive learning model, and the independent trace model) of sequential effects in psychophysical tasks. These models were tested using data from a study by W. S. Verplack et al (see record 1953-04864-001). The models appear to be most consistent with the independent trace model in which the momentary value of the criterion is modified by memory traces, an independent trace being retained for each relevant past event. On this basis, a theory of criterion setting is developed: A long-term process determines an initial value for the criterion, and 2 short-term processes adjust the criterion to match current changes in the expected probabilities of signals and to maximize the information transmitted by the S's responses. The theory is applied to results in the literature. (65 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial frequency discrimination: visual long-term memory or criterion setting?

A long-term sensory memory is believed to account for spatial frequency discrimination when reference and test stimuli are separated by long intervals. We test an alternative proposal: that discrimination is determined by the range of test stimuli, through their entrainment of criterion-setting processes. Experiments 1 and 2 show that the 50% point of the psychometric function is largely determined by the midpoint of the stimulus range, not by the reference stimulus. Experiment 3 shows that discrimination of spatial frequencies is similarly affected by orthogonal contextual stimuli and parallel contextual stimuli and that these effects can be explained by criterion-setting processes. These findings support the hypothesis that discrimination over long intervals is explained by the operation of criterion-setting processes rather than by long-term sensory retention of a neural representation of the stimulus.     

Implications of visual search deficits for cognitive theory.

Neuropsychological evidence was presented and found to be consistent with Treisman's Feature Integration Theory (FIT). Several studies were reported using groups of patients with unilateral visual neglect, stable patients with known lesion loci, and a single patient with bilateral parietal-occipital lesions. Collectively, the data support a distinction between feature and conjunction search. They also support arguments for the primary role of spatial representation in forming correct conjunctions between features and for individuating objects. Nevertheless, the data do call for some refinements in FIT. The spatial maps involved in feature integration for serial visual search and for the experience of an accurately conjoined object appear to be relatively late. Features are likely to be integrated in the nervous system at sub-threshold levels in early vision (e.g., vl or v2), but it requires supra-threshold spatial knowledge to successfully conjoin features in visual experience (Wojciulik, Robertson & Kanwisher, 1994). The evidence as a whole, however, is consistent with FIT in that spatial information is necessary for controlled visual search and for the accurate conjunction of features in multi-item arrays. In addition, it suggests that explicit access to relatively late spatial information is necessary to correctly conjoin features in the experiences percept. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of surface medium on visual search for orientation and size features.

By using a visual search task, this study examined the encoding of orientation and size for stimuli defined in five different surface media: luminance, color, texture, relative motion, and binocular disparity. Results indicated a spatially parallel analysis of size and orientation features for all surface media, with the possible exception of binocular disparity. The data also revealed a search rate asymmetry in the orientation task for all media: Parallel or shallow search functions were obtained for oblique targets in vertical distractors, whereas steeper serial search functions were obtained for vertical targets in oblique distractors. No consistent asymmetry was found for the large and small targets in the size task. There seemed to be common principles of coding in all these different media, suggesting either a single analysis of shape features applied to a common representation or multiple analyses, one for each surface medium, with each extracting a similar set of features. The shared coding principles may facilitate the use of redundancy across media to reduce ambiguities in the locations and shapes of contours in the visual scene. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conjunction search revisited.

Search for conjunctions of highly discriminable features can be rapid or even parallel. This article explores three possible accounts based on (a) perceptual segregation, (b) conjunction detectors, and (c) inhibition controlled separately by two or more distractor features. Search rates for conjunctions of color, size, orientation, and direction of motion correlated closely with an independent measure of perceptual segregation. However, they appeared unrelated to the physiology of single-unit responses. Each dimension contributed additively to conjunction search rates, suggesting that each was checked independently of the others. Unknown targets appear to be found only by serial search for each in turn. Searching through 4 sets of distractors was slower than searching through 2. The results suggest a modification of feature integration theory, in which attention is controlled not only by a unitary "window" but also by a form of feature-based inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Binding in short-term visual memory.

The integration of complex information in working memory, and its effect on capacity, shape the limits of conscious cognition. The literature conflicts on whether short-term visual memory represents information as integrated objects. A change-detection paradigm using objects defined by color with location or shape was used to investigate binding in short-term visual memory. Results showed that features from the same dimension compete for capacity, whereas features from different dimensions can be stored in parallel. Binding between these features can occur, but focused attention is required to create and maintain the binding over time, and this integrated format is vulnerable to interference. In the proposed model, working memory capacity is limited both by the independent capacity of simple feature stores and by demands on attention networks that integrate this distributed information into complex but unified thought objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual memory for novel shapes: Implicit coding without attention.

Implicit memory for novel shapes was explored with a negative priming paradigm. The results show that representations of shapes, formed in a single trial and without attention, can last without decrement across 200 intervening trials and with temporal delays of up to a month. No explicit memory of the shapes was available, either immediately or after a delay. There were consistent individual differences in the amount of negative priming shown, and some participants showed only facilitation. There was a trend toward increased facilitation across time, as if the memory of the shape survived longer than an "action tag" attached to it, which specified whether it should be attended or ignored. The results demonstrate a surprising combination of plasticity and permanence in the visual system and suggest that the roles of both attention and repetition may be to ensure voluntary retrievability rather than to form a lasting memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effectiveness of psychiatric treatment for HIV-infected patients

p-hydroxymethamphetamine (OHMAP) is one of the major metabolites of the widely abused drug methamphetamine (MAP). The demethylation of OHMAP to p-hydroxyamphetamine (OHAP) has been shown in vitro but has never been reported in vivo. The disposition kinetics as well as the metabolism of OHMAP was investigated employing a sensitive HPLC method which can separate the enantiomers of OHMAP and OHAP. Both conjugated and unconjugated forms of these compounds can be quantitated. Male Sprague-Dawley rats were given an iv bolus of racemic OHMAP (20 mg kg-1) and serum and urine samples were collected at selected times. The serum concentration-time data for OHMAP enantiomers could be described by a biexponential equation. The clearance of D-OHMAP (93.5 mL min-1 kg-1) was slightly, but statistically significantly, greater than that of the L-enantiomer (83.9 mL min-1 kg-1). The steady-state volumes of distribution of L- and D-OHMAP were (mean +/- SD) 3.15 +/- 0.84 and 4.23 +/- 1.76 L kg-1, respectively. No significant concentrations or amounts of OHAP enantiomers could be detected in any serum or urine sample. Rats excreted more unchanged L-OHMAP (34%) than D-OHMAP (29%). In contrast, more conjugated D-OHMAP (57%) was recovered compared to the conjugated L-OHMAP (52%). The results suggest that there is slight stereoselectivity in the disposition of OHMAP enantiomers. The N-demethylation product (OHAP) was not produced in vivo.