Three experiments were designed to investigate outstanding questions concerning the effect of memory load variations on efficiency and coding processes in the left and right cerebral hemispheres. In Experiment 1 subjects were presented with one, two, or three target letters in uppercase or lowercase in central vision, followed by simultaneous bilateral probes requiring a name match response. Twenty young right-handed adults, 10 males and 10 females, acted as subjects. Two main features of the results were as follows: (a) The slope of the linear function relating mean reaction time (RT) and set size was 30% greater for right visual field (RVF)-left-hemisphere probe stimuli under both physical and name identity conditions, and (b) RT for RVF-left-hemisphere probes was greater when the probe was drawn from preterminal serial position in the target list. Experiments 2 and 3 examined the proposition that the results of Experiment 1 reflected asymmetric interference during list acquisition. The results showed that, first, the LVF-right-hemisphere advantage was eliminated or reversed under unilateral probe presentation conditions, and second, the LVF-right-hemisphere advantage for a single, preterminal serial position was insensitive to variations in the interitem interval. The results are thought to be inconsistent with the interference hypothesis. The general implications of the results for existing theories of hemisphere function are discussed.

Adolescent↗

PubMed1979

Visual persistence and code selection in short-term memory for letters.

Four experiments were conducted to examine temporal changes in visual and name codes and the relationship between them. Unlike earlier studies, the design included (a) several levels of visual similarity in addition to the conventional same case and different case conditions and (b) physical- as well as name-match tasks to provide direct evidence about subjects' retention of form information. The main results were as follows: First, the presence of multiple typefonts in the stimulus set does not eliminate convergence between the reaction time functions for the physical- and name-match conditions in a name-match task. Second, inclusion of a physical-match task, requiring subjects to retain form information, does not necessarily eliminate convergence in a primary, name-match task. When the secondary task does reduce convergence, however, the results suggest that it does this through its effect on the name-match function rather than on the physical-match function. Third, apart from difficulties with within-cluster typefont combinations, particularly at long interstimulus intervals, subjects can generally retain and use reliable information about letter form over the ISI range (.5--4.0 sec) used in the experiments. The results were thought to be consistent with the conclusion that convergence results from a combination of (a) a nonoptional decrease in the accessibility of the visual code as a function of increasing ISI and (b) an optional increase in the accessibility of the name code. Under ISI conditions at least, convergence cannot be attributed to either generation of a visual code of the alternative form of the target letter or to the absence of relevant form information.

Discrimination Learning↗

PubMed1974