The role of attention in perceptual learning has also been studied using electrophysiological recordings in behaving animals (Li et al.,
2004; Op de Beeck, Wagemans, & Vogels,
2007; Polley, Steinberg, & Merzenich,
2006). For example, Polley et al. (
2006) trained rats to attend to independent parameters: either frequency or intensity of an identical set of auditory stimuli. The results showed that the presence of irrelevant information (e.g., frequency information while attending to intensity) did not lead to learning of the irrelevant information. At first sight, these electrophysiological results—together with the earlier behavioral finding of Ahissar and Hochstein (
1993)—appear to be at odds with the results of Watanabe et al. (
2001). However, Polley et al. (
2006) give a possible explanation for the discrepancy: In Watanabe's case the task-irrelevant information was presented at a sub-threshold level, whereas in their own case, the task-irrelevant information was at a supra-threshold level. They propose that “plasticity is restricted to the task-relevant domain only if stimuli in the task-irrelevant domain interfere with the ability to solve the task” (Polley et al.,
2006, p. 4981). Support for this proposition comes from a recent study by Tsushima, Sasaki, and Watanabe (
2006). In this study, observers performed a RSVP task in the presence of motion with variable strength. Performance on the RSVP task was maximally impaired when the strength of the motion was at a sub-threshold level. Interestingly, the lateral prefrontal cortex (LPFC), presumably involved in exerting inhibitory control of irrelevant signals (Dias, Robbins, & Roberts,
1996; Kerns et al.,
2004; Knight, Staines, Swick, & Chao,
1999) became active when the motion strength was above perceptual threshold. The authors suggest that LPFC is involved in suppressing task-irrelevant signals: With supra-threshold motion, area LPFC inhibits the irrelevant motion; with sub-threshold motion, however, LPFC remains inactive, leaving the irrelevant signals uninhibited.