New Variations of Intrahemispheric and Interhemispheric Processing Indexed by the Dimond Paradigm

Abstract

We report 2 experiments designed to demonstrate that unilateral tachistoscopic stimulation would yield a response time (RT) advantage over bilateral stimulation in a simple experiment, whereas the opposite pattern would occur in a complex version of the same task, as predicted by the intrahemispheric resource limitation model of Banich and colleagues. Experiment 1 was a go/no-go task in which participants had to press a key when two shapes (circles or squares) were identical on the computer screen. A unilateral field advantage was obtained that was accentuated in several task conditions that yielded overall longer RTs, mostly in the bilateral condition. Experiment 2 was similar but required a more complex judgment: The go trials were to 2 stimuli identical on 1 dimension (shape or color) but not both or neither. The RTs were significantly and substantially longer than in Experiment 1 and exhibited a nonsignificant bilateral field advantage, which differed significantly from the unilateral field advantage obtained in Experiment 1. These results support the intrahemispheric resource limitation model of Banich and colleagues. However, several within-experiment effects are in direct opposition to this model and are best explained as limitations of commissural relay of perceptual information.

Inter-hemispheric dynamics revealed by reaction time in the Dimond paradigm

“…However, an effect observed only on bilateral trials is more likely to capture an adaptation specific to the inter-hemispheric commissure. The result obtained by Braun et al (2011), greater adaptation in bilateral trials, therefore provisionally appears to be attributable to callosal network plasticity. This plasticity could be of several sorts.…”

“…Using this line of reasoning, Desjardins and Braun (2006) and Braun et al (2011) tried to determine whether tachistoscopic visual stimulation and collection of RTs would reveal such an effect. They predicted that placing two stimuli to be discriminated in an oblique rather than a horizontal axis (relative to the meridian) on a computer screen (see Figure 1 for an illustration) should present a cost in RT significantly greater in bilateral stimulation conditions (requiring inter-hemispheric integration) than in unilateral stimulation conditions (not requiring inter-hemispheric integration).…”

“…Accordingly, the experiments in question did not seek to perfectly balance out eccentricity of all stimuli, nor have they controlled for homotopy or analysed practice effects in a single condition. Braun et al (2011) found in their first experiment that practice on the task shortened RTs in general and changed the balance of RTs in unilateral and bilateral field stimulation conditions in an unexpected direction (c.f., Banich & Belger, 1990, reviewed above), i.e., towards a smaller UFA. The Braun et al (2011) finding, observed in a simpler perceptual matching task (RT was in the 300-500 ms range), is diametrically opposed to the intra-hemispheric resource limitation effect.…”

“…Braun et al (2011) found in their first experiment that practice on the task shortened RTs in general and changed the balance of RTs in unilateral and bilateral field stimulation conditions in an unexpected direction (c.f., Banich & Belger, 1990, reviewed above), i.e., towards a smaller UFA. The Braun et al (2011) finding, observed in a simpler perceptual matching task (RT was in the 300-500 ms range), is diametrically opposed to the intra-hemispheric resource limitation effect. With practice, the RT became shorter, but the unilateral/bilateral balance of RTs did not move toward a larger UFA, as would be predicted by the intrahemispheric resource limitation model.…”

“…Secondly, their Experiment 2 could not distinguish the extent to which local/global orientational conflict caused the shift from a UFA to a BFA. In the Braun et al (2011) study, the square stimuli had oriented contours (horizontal and vertical). We term this aspect of orientation "local".…”