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A cognitive process model is developed that predicts the 3 major symbolic comparison response time effects (distance, end, and semantic congruity) found in the results of the linear syllogistic reasoning task. The model assumes that people generate an ordering of a finite set of symbolic stimuli on the basis of information contained in the pairwise relations between adjacent stimulus items. The learning of this ordering is simulated within a simple connectionist framework. The decision-making component of the model utilizes 2 separate evidence accrual processes operating in parallel. One process accumulates information about the positional difference between the stimulus items being compared, and the other accumulates information about the endpoint status of each of those items. A response occurs whenever enough evidence favouring it has been accumulated within either of these processes. The model also assumes that the congruencies between the positions of the stimulus items within the ordering and the form of the comparative instruction can lead to either interfering or facilitating effects on the rate of evidence accumulation within each of these accrual processes. To test the model, data are obtained from the single-session performances of a group of 16 subjects and the multiple-session performances of an additional 2 subjects. The task is a variant of the one used by Trabasso, Riley, and Wilson (1975) and involves paired comparisons of ordered symbolic stimuli (three-letter names). Simulations of the model provide an excellent account of the group mean correct response times, as well as a very good account of the full set of data obtained from the 2 additional subjects (including percentage correct and response time distributional data).

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Thesis (Ph. D.)--Open University.

An empirical exploration of factors that facilitate priming in young children was undertaken utilizing sequentially degraded pictures (fragpix) developed by Snodgrass and her colleagues. The identification of fragmented pictures was studied by 288 children across four experiments. In the first two experiments abbreviated sets of fragpix were generated for use with young children. Experiments 3 and 4 manipulated five attributes of the priming stimulus to measure their effect on direct and indirect tests of memory. Experiment 3 was a scaling study that delineated age associated identification thresholds for fragpix. It also examined hypotheses regarding the impact of prior exposure and perceptual closure on indirect and direct tests of memory. During the exposure and test condition, 3-, 4-, 5- and 8-year olds were shown fragpix in descending degrees of fragmentation until they correctly named the picture. Snodgrass proposed perceptual closure as an explanatory mechanism for identification of incomplete pictures. To explore this hypothesis, following identification of each fragpic, half the children were shown the completed picture. This manipulation had no facilitative effect on identification or recall of fragmented pictures. Two measures of prior exposure, priming and transfer, were also computed. Age differences were found on picture identification, free recall, and picture recognition measures of discrimination and response bias. A linear trend was revealed on measures of priming for picture identification, and for picture recognition but not for recall. A similar method was used for each of the first three experiments: Fragpix were presented in their most degraded form with pictorial information systematically added until the picture was named. Snodgrass and Feenan (1990) suggested that priming might be equally effective if only single levels of fragmentation were presented. They reported that exposing adults to moderately fragmented pictures promoted closure and was more beneficial for later identification, than exposure to maximally-fragmented or nearly completed pictures. Experiment 4 tested this "optimal level" hypothesis with 5- and 8-year olds. Scores from Experiment 3 were used to select age-specific levels of fragmentation that made fragpix easy, moderately easy, or difficult to identify. Attributes of the priming stimulus were manipulated in Experiment 4 to examine the differential impact of varying exposure conditions on performance and on the magnitude of priming. Three manipulations occurred: One varied number of stimulus changes across levels of fragmentation, a second varied order of difficulty, and a third varied the nature of stimulus change (random or systematic). Manipulating the priming stimulus influenced fragpix identification and priming, but had little definitive impact on free recall. For both ages stimuli presented in a systematic rather than random order facilitated picture identification and the magnitude of priming. In addition, developmental differences emerged among systematic orders of presentation. Five-year-olds demonstrated optimal performance in picture identification and measures of picture recognition when there were multiple changes in temporal contrast, while order of difficulty (moderate to easy to hard) was more facilitative for 8-year-olds. A finding for a quadratic function for 8-year-olds on picture identification and magnitude of priming supported a moderately fragmented stimulus being an optimal prime, while for 5-year-olds, the relationship was monotonic. This pattern was not observed on the direct memory tests. It is argued that both perceptual and cognitive components of the task influence performance in an integrative manner on indirect and direct memory tests. A modified form of transfer appropriate processing is proposed as a reasonable explanation of the findings. / Graduate

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