The role of attention in visual bilateral matching tasks.

The consistent finding of studies employing visual matching tasks has been a reaction time and accuracy advantage for judgements about stimuli presented bilaterally when compared to the average performance of the two unilateral field presentations. As with recent studies showing the influence of attention on reaction times to unilateral presentations, we hypothesized that attentional mechanisms may also play a role in the speed advantage seen with bilateral letter presentations. The present study employed random dot-patterns ("dot-primes"), presented in the upper half of the LVF, RVF, Bilateral VF, or absent, as abrupt onset peripheral cues to attract attention automatically. Letter pairs followed immediately (14 msecs) after the dot-primes in the lower half of the LVF, RVF, or Bilateral VF. The results for unilateral dot-primes, followed by unilateral letter pairs, were consistent with previous studies showing that the field advantage for a particular task can be altered using abrupt onset attentional cues, with the advantage going to the field where the attentional prime is presented. Bilateral dot-primes did reduce latencies to subsequent bilateral letter pairs, but bilateral primes also reduced latencies to both LVF and RVF letter pairs, in nearly the same proportion as for bilateral letter pairs. Latencies for RVF-primes/Bilateral-letters were as fast as for Bilateral-primes/Bilateral-letters, and both of these conditions were significantly faster than LVF-primes/Bilateral-letters. The results suggest that attention plays a relatively minor role in the bilateral field advantage, and that non-attentional factors (i.e. interhemispheric dynamics) account for most of the asymmetric unilateral-prime influence on bilateral performance. Possible interhemispheric factors which may contribute to these results are discussed.

The bilateral field advantage on a letter-matching task.

A series of studies have reported that responding is faster when letter pairs to be matched are projected to two hemispheres rather than one. Four experiments described here tested this bilateral field advantage and identified factors that influence its extent. Subjects were shown letter pairs drawn from the ensemble "AaBb", and classified the letter pairs as "Match" if the letters had the same name (regardless of case) and "No Match" if they did not. In the first two experiments the letter pairs were presented unilaterally (both letters in one visual field), bilaterally (one letter in each visual field), or centrally (both letters on the vertical midline, above and below fixation), in order to investigate how the bilateral field advantage is influenced by screen location. The third experiment added a bilateral-diagonal position (to check for artefacts related to horizontal scanning strategies), and the fourth experiment added distractor digits (to equate initial processing demands in the bilateral and unilateral conditions). Results indicate that the bilateral field advantage is a robust phenomenon, although several manipulations reduced its magnitude. Implications of these findings for models of hemispheric collaboration and interhemispheric processing are discussed.

Hemispheric interactions: the bilateral advantage and task difficulty.

Twenty-five normal subjects made "same-different" responses to dot patterns presented in the LVF, RVF or bilaterally. Task difficulty was manipulated in each condition by varying the number of dots in the two patterns presented from two to four to six. The pairs of patterns always had the same number of dots on a given trial. Response latency and accuracy worsened as the number of dots increased for all three presentation conditions and for both "same" and "different" judgements. Overall, responding was faster and the number of errors lower on Bilateral presentations. For response latencies to identical patterns of dots, the size of the bilateral advantage increased relative to RVF responding as task difficulty increased but did not change significantly relative to LVF responding. When the two patterns were not identical the size of the advantage did not change as task difficulty increased. "Same" judgements were faster but less accurate than "different" judgements. A model of hemispheric interactions is proposed to account for the findings.

Three versions of the additive theories of behavioral contrast.

The additive theories of behavioral contrast state that contrast will occur only when two types of responses interact during multiple schedules. Three more specific versions of the theories may be defined according to how they distinguish these two types of responses. A strong version physically distinguishes them. A second version distinguishes them according to the theoretical processes which control them. A weak version distinguishes them on the basis of the environmental relations which control them. Only the weak version of the theories is currently testable. The weak theory should be tested by establishing each of the two environmental relations independently and then combining them to assess their effect on behavior. Because this test is not usually performed, many of the results which have been taken to support or contradict the additive theories are actually ambiguous.

Contrast and undermatching as a function of reinforcer duration and quality during multiple schedules.

Eight pigeons pecked keys under multiple variable-interval two-minute variable-interval two-minute schedules. In Experiment 1, the reinforcers were 2, 4, or 8 seconds access to a food magazine. In Experiments 2 and 3, the reinforcers were grains that had been determined to be most-, moderately-, or non-preferred. Both positive and negative behavioral contrast occurred when the reinforcers in one component were held constant and the duration or type of reinforcer obtained in the other component varied. Undermatching occurred when the relative rate of responding during a component was plotted as a function of the relative duration of the reinforcers in that component.

Defining behavioral contrast for multiple schedules.

Two different definitions of behavioral contrast have been used for multiple schedules. One, interschedule, definition identifies contrast as changes in the rates of responding which occur when subjects move from one multiple schedule to another. The other, intraschedule, definition emphasizes changes in the rates of responding which occur relative to a baseline rate of responding. The baseline is the rate of responding emitted during a multiple schedule that supplies equal rates of reinforcement in the two components. The distinction between these two definitions is important for empirical and theoretical reasons. For example, theoretical confusion has arisen when the interschedule definition has been used to test and reject theories which implicitly define contrast by the intraschedule definition.

Matching, contrast, and equalizing in the concurrent lever-press responding of rats.

Five rats pressed levers for food reinforces delivered by several concurrent variable-interval variable-interval schedules. The rate of reinforcement available for responding on one component schedule was held constant at 60 reinforcers per hour. The rate of reinforcement available for responding on the other schedule varied from 30 to 240 reinforcers per hour. The behavior of the rats resembled the behavior of pigeons pecking keys for food reinforcers. The ratio of the overall rates of responding emitted under, and the ratio of the time spent responding under, the two components of each concurrent schedule were approximately equal to the ratio of the overall rates of reinforcement obtained from the components. The overall rate of responding emitted under, and the time spent responding under, the variable component schedule varied directly with the overall rate of reinforcement from that schedule. The overall rate of responding emitted under, and the time spent responding under, the constant component schedule varied inversely with the overall rate of reinforcement obtained from the variable component. The local rates of responding emitted under, and the local rates of reinforcement obtained from, the two components did not differ consistently across subjects. But they were not exactly equal either.