Expanding the search for a linear separability constraint on category learning

Formal models of categorization make different predictions about the theoretical importance of linear separability. Prior research, most of which has failed to find support for a linear separability constraint on category learning, has been conducted using tasks that involve learning two categories with a small number of members. The present experiment used four categories with three or nine patterns per category that were either linearly separable or not linearly separable. With overall category structure equivalent across category types, the linearly separable categories were found to be easier to learn than the not linearly separable categories. An analysis of individual participants' data showed that there were more participants operating under a linear separability constraint when learning large categories than when learning small ones. Formal modeling showed that an exemplar model could not account for many of these data. These results are taken to support the existence of multiple processes in categorization.     

Bogus concerns about the false prototype enhancement effect

Two experiments addressed the mechanism responsible for the false prototype effect, the phenomenon in which a prototype gradient can be obtained in the absence of learning. Previous demonstrations of this effect have occurred solely in a single-category paradigm in which transfer patterns are assigned or not to the learning category. We tested the hypothesis that any extraneous variable potentially responsible for this effect, such as compactness varying with pattern distortion (Zaki & Nosofsky, 2004), may be functional in the single-category paradigm but not when multiple categories are available at the time of transfer. In the present study, subjects received a bogus or a real category learning phase, followed by a transfer test that required assignment into 1 or 3 prototype categories. The results showed that a minimal prototype gradient was obtained in the bogus conditions, with performance approaching chance levels when classification into 3 categories was required. In contrast, a substantial prototype gradient effect was found following learning. We conclude that the prototype gradient typically obtained following multiple-category learning is primarily driven by real learning and that the false prototype effect is itself an artifact of the single-category paradigm.     

The enduring effect of availability

The present study addressed whether experienced ease of retrieval of autobiographical events affects trait judgments made immediately and after a delay (Experiment 1) and whether this influence is modulated by either of two discounting instructions (Experiment 2). In Experiment 1, participants first attempted to retrieve 6 or 12 personal memories for different traits and then made ease of retrieval and self-trait judgments immediately or 1 week later. In Experiment 2, participants made immediate ratings and then delayed ratings under 3 instructional manipulations: a generic instruction to repeat these judgments, to make these ratings after they were reminded of their original recall total, or to make these ratings after they had their retrieval ease discounted or augmented. In each experiment, an enduring effect of availability was obtained in that the relationship between ease of retrieval and self-trait rating was only slightly affected by the delay. Being reminded of the original number of recalled memories nullified the relationship between ease of retrieval and trait rating. However, discounting or augmenting ease of retrieval, which altered ease of retrieval ratings, did not. Potential explanations for an enduring effect of availability are discussed.     

Correlation between Changes in Stress-Induced Corticosterone Secretion and GR mRNA Levels

The current study was conducted to determine the potential relationship between stress-induced corticosterone secretion and corticosteroid receptor mRNA levels after 5 days of intermittent stress. In particular, we were interested in the rate at which animals terminate a stress response, and how this termination may be altered by repeated stress. Adult male Sprague-Dawley rats were subjected to either 5 days of restraint stress or 5 days of an unpredictable stress paradigm. Restraint-stress induced corticosterone secretion was measured on Days 1 and 5 in both groups, and animals were killed on Day 6. Glucocorticoid receptor (GR), and mineralocorticoid (MR) mRNA levels were determined using in-situ hybridization techniques. Five days of restraint stress caused an habituation of the plasma corticosterone response to stress measured 60 and 90 min post-stress initiation; this pattern of corticosterone secretion was not observed in the animals subjected to unpredictable stress. Five days of either stress paradigm did not alter MR mRNA levels measured within the hippocampus or GR mRNA levels within the hippocampus or the medial parvocellular division of the paraventricular nucleus of the hypothalamus (mpPVN). However, an individual's GR mRNA levels measured within the CA1/2 region of the hippocampus and the mpPVN were significantly correlated with the degree of habituation of the corticosterone response to stress measured on Day 5. This suggests that an increase in the rate of termination of the stress response and levels of GR within the hippocampus and mpPVN may be functionally related.     

Personality patterns of white,black, and Mexican-American patrolmen as measured by the Sixteen Personality Factor Questionnaire

The Sixteen Personality Factor Questionnaire was administered to 461 Los Angeles patrolmen to abtain a normative police profile. Multivariate analysis revealed that the average patrolman appeared brighter, more reserved, dominant, and tough-minded (p less than .001) than the average male. Comparisons were made for 29 black, 33 Mexican-American, and 399 white officers. Mexican-American officers emerged as more conservative and relaxed than whites, while black officers appeared more experimental, analytical, and group-oriented. A comparison with an idependent police sample revealed common traits of self-assurance and conservatism. Results were compared with a social workers' profile and discussed in relation to police officers' actual job activities and community needs.     

Triadic decision making in lexical memory

Word and category recognition was investigated in the context of other stimuli, where the semantic distance relationships among the stimuli were derived from multidimensional scaling. On each trial, three horizontal strings of letters were presented. In the word condition, a positive response was required when the three strings formed three words; in the category condition, a positive response was required when the three strings formed words belonging to the same category. The results indicated that: (a) category decisions take about 150-200 msec longer than do word decisions, (b) word decisions are facilitated by a common categorical membership but semantic distances within the category are relatively unimportant, and (c)within-category semantic distances systematically altered response time for the category condition. It was hypothesized that semantic distance relationships may be sensitized for categorical decisions, but that only large semantic distances function effectively for word decisions.     

Organization and long-term memory search

A recognition RT paradigm was used to assess a number of plausible search strategies in LTM for categorized lists. List length was determined by factorially combining two, three, or five categories with two, three, or five words per category, and test items could be one of four types: (1) positive, (2) a repeated positive, (3) a related negative, or (4) an unrelated negative. It was found that RT increased linearly with category size for both positive and related negatives (about 30-40 msec/item); whereas the increase was much smaller for the unrelated negatives, especially for three and five categories (about 9 msec/item). With an increase in the number of categories, RT increased at the rate of about 40 msec/category for all three test items. A theory of .high-speed scanning for categorized material was proposed in which a serial and exhaustive search of the categories, is first undertaken. If a positive category match is found, a serial and exhaustive search within the contents of the positive category is initiated; if no category match is found, the search is simply terminated. Some evidence was presented that categories recently probed may provide for a short-circuiting of the category search.     

Reallocation of visual attention.

Attentional movement time was investigated within and across hemifields in a discrimination task in which retinal acuity was controlled. Ss discriminated targets in a two-alternative, forced-choice latency paradigm. In Experiments 1-3, costs were mediated by distance, even though it was varied independently of acuity. In Experiments 4 and 7, with distance held constant, costs were equivalent for crossing the vertical and horizontal meridians and for crossing 1 and 2 meridians. However, crossing 1 meridian produced costs that were less than the costs for shifts to unexpected locations in the same quadrant, partially replicating the inhibitory aftereffect of Tassinari, Aglioti,Chelazzi,Marzi,and Berlucchi (1987). An explanation based on a combination of analog movement (Tsal, 1983) and attentional distribution (Downing & Pinker, 1985; Hughes & Zimba, 1987; Tassinari et al., 1987) models was discussed.     

Memory search following valid and invalid abrupt-onset cues

The impact of abrupt-onset cues on memory search was investigated, where the abrupt-onset cue was a valid (Experiment 1), random (Experiment 2), or irrelevant (Experiment 3) predictor of the location containing the test probe. In Experiment 4, the abrupt-onset cue either preceded or followed the test probe. Sternberg-like functions were obtained in Experiments 1 and 2, with the effects of the abrupt-onset cue localized primarily in the intercept rather than the slope. Experiment 3 demonstrated that a spatially separated and irrelevant abrupt-onset cue increased latency even when all memory probes occurred at the fixation point. In Experiment 4, the robust impact of an abrupt-onset cue vanished, regardless of stimulus onset asynchrony, when it followed the target. We concluded that abrupt-onset cues captured attention regardless of their predictability, manifested as a delaying of search. However, once attention was captured by the target, a subsequent abrupt-onset stimulus had no effect. These results were discussed in terms of diffuse attention and contingent capture models of attention.