The effects of varying levels of hemispheric activation on episodic memory.

Bilateral saccadic eye movements enhance episodic memory retrieval; however, this usually only occurs for consistent-handed, not inconsistent-handed, individuals. It was hypothesized that inconsistent-handers begin closer to the peak of a Yerkes-Dodson-type inverted-U curve and increasing activation pushes them along the curve eventually decreasing performance, while consistent-handers start at a lower baseline and therefore increasing activation increases their performance. The current study tested this hypothesis by using hand clenching (grip strength) to increase activation at 5 different levels for both consistent- and inconsistent-handers. A total of 316 participants were presented with a list of 36 words after which they squeezed a hand dynamometer to induce cortical activation, and then recalled as many of the words as they could. Results showed that, as predicted, both inconsistent- and consistent-handers demonstrated an inverted-U pattern of memory performance as the strength of squeeze increased with inconsistent-handers peaking at a lower level of grip strength than consistent-handers. These results may help explain past findings, not only with episodic memory but also a variety of other cognitive tasks. They may also have interesting theoretical and real-world implications, which are discussed.