James T. Townsend Lab
Department of Psychology
It has long been of interest to psychologists as to whether the items were processed simultaneously (i.e., in parallel) or sequentially (i.e., serially). Although certain types of parallel and serial models have been ruled out, it has not been possible to entirely separate serial and parallel models in typical data. Recent advances in theory-driven methodology now permit strong tests of serial vs. parallel processing in rapid scanning for a target in short-term and visual-search tasks. Methodology involving factorial variation in order to determine mental architecture and to assess processing capacity has been greatly expanded over the past several decades. We challenge previous ideas using double factorial paradigm designed to test architectural properties of memory-search and visual-search tasks.
1. Visual Search (James Townsend, Mario Fific)
Basic task included visual search for two complex stimuli (pseudowords). Visual similarity of each item to the target was manipulated. Both Mean and Survivor interaction contrast indicated overall overadditivity in processing. Typical signatures of standard serial and parallel processing were not observed.
Also additional experiments indicated that additivity and consequentially seriality could be observed when either mutual visual similarity of the search items is reduced or when processing is forced to be serial by sequential presentations of the search set.
Several models were tested that includes possible dependency between processes, different mixtures of serial and parallel and model with interaction between items in the search set. Both Serial and Parallel processing models exhibit similar predicative behavior under specific set of assumptions and fit the data well.
[2004 OHIO HML talk: Proposed model for efficiency variability in a visual search task]
Methodology involving factorial variation in order to determine mental architecture and to assess processing capacity has been greatly expanded over the past several decades. However, it has never been adapted to study the realm where much of the interest began in the 1960s: short-term memory search. We present a new method of manipulating probe-to-memory item processing speed and our initial results for loads n=2,4. Three variables were manipulated in this experiment: number of processing elements (2), phonemic dissimilarity of a target to the particular memorized element (high, low) and duration between memorized set and a target (short-long). We employ the recent results involving the distribution functions rather than means alone. Our results suggest that some observers really are serial whereas others are strongly parallel. Thus, these fine grained analyses portend quite striking individual differences in this basic cognitive task.