CONTEXTUAL EFFECTS AND ASSOCIATIVE PROCESSES IN COMPARATIVE JUDGEMENTS WITH PERCEPTUAL AND SYMBOLIC STIMULI

In each of three experiments, participants first learned to associate nonsense syllables (CVCs) with visual extents. In the first two experiments, these labels were then used as standards in the method of constant stimuli. Weber fractions for the remembered standards exhibited endpoint effects and systematically varied with set size, range, and acquisition conditions. In the third experiment, the additive factors methodology was used to permit a strong test of the propositionally based stage models of symbolic comparisons. Extending the developing area of memory psychophysics, Baranski and Petrusic (1992) applied the classic method of constant stimuli with remembered standards to determine, directly, the precision and the accuracy of the long memory representations of percepts. As in the landmark memory psychophysics experiment (Bjorkman, Lunberg & Tarnblom, 1960), participants in the Baranski and Petrusic experiments first learned to associate a label (a CVC) with each element in a set of perceptual magnitudes using traditional paired associate training methods. In the second phase, each of the CVC's was presented as a standard together with a variable perceptual comparison stimulus using the method of constant stimuli . Psychometric functions were then obtained for each subject with each standard (St) in order to obtain estimates of the Just Noticeable Difference (JND), Weber Fraction (WF=JND/St), and the Point of Subjective Equality (PSE). Baranski and Petrusic (1992) argued that their findings provided considerable support for the view that the elementary, unidimensional, aspects of sensory experience are preserved in memory in a format closely analogous to their representation in perception, albeit less precisely. The present experiments are motivated by a natural extension of this noisy-analogue position; namely, that the units representing the long-term memories of unidimensional percepts, such as visual extent, for example, are organized in an array in which underlying perceptual similarity is preserved through proximity of memory analyzers, and neigbouring units laterally inhibit one another, with increasing inhibition with proximity of the analyzers. The present experiments extend our earlier work by examining the effects of variations in the context of the memory ensemble. The examination of global contextual effects takes two forms. In the first experiment, the number of stimuli i n the memory ensemble is varied. Range effects, arising from variations in the spacing of the alternatives along the underlying perceptual continuum, are examined in the second experiment. Acquisition processes are also studied. Experiment 2 was designed to determine if over learning of the association between label and percept decreases putative lateral inhibition and, consequently, increases memory precision. The third experiment was designed to provide a test of the additive stages models of symbolic comparisons by controlli ng the degree of remoteness of association from label to percept. Participants learned to associate another label (remoteness level 2) with the label originally associated (remoteness level 1) with the percept and subsequently made symbolic comparisons at each remoteness level. EXPERIMENT 1 Although set size effects are evident in short-term memory (STM) search, the STM distracter paradigm, long-term memory, visual search, and in the classic serial li st learning paradigms, they remain to be studied in memory psychophysics. The present experiment was conducted with a view toward determining the precise dependence of the quality of the representation in memory on the number of elements in memory; i.e., on set size. The extended noisy-analogue view, suggests that as the size of the memory ensemble increases, the amount of lateral inhibition any memory unit receives increases, and thus increases in set size must necessarily result in diminished memory precision for each element in the larger ensemble. Perceptual comparisons should not exhibit set size effects since perceptual analyzers are much more finely tuned than memory analyzers.