The influence of perceptual and semantic categorization on inhibitory processing as measured by the N2-P3 response

Abstract

In daily activities, humans must attend and respond to a range of important items and inhibit and not respond to unimportant distractions. Our current understanding of these processes is largely based on perceptually simple stimuli. This study investigates the interaction of conceptual-semantic categorization and inhibitory processing using Event Related Potentials (ERPs). Participants completed three Go-NoGo tasks that increased systematically in the degree of conceptual-semantic information necessary to respond correctly (from single items to categories of objects and animals). Findings indicate that the N2 response reflects inhibitory processing but does not change significantly with task difficulty. The P3 NoGo amplitude, on the other hand, is attenuated by task difficulty. Further, the latency of the peak of the P3 NoGo response elicited by the most difficult task is significantly later than are the peaks detected during performance of the other two tasks. Thus, the level of complexity of conceptual-semantic representations influences inhibitory processing in a systematic way. This inhibition paradigm may be a key for investigating inhibitory dysfunction in patient populations.

Figures

Figure 1

Sample of stimuli used across all four inhibition tasks. Go items were shown 160 times, or 80%, while NoGo were shown 40 or 20%. For the Standard and Single tasks these specific items were repeated 160 and 40 times. For the Multiple and Semantic conditions there are example items taken from the larger set.

Figure 2

N2 and P3 Go and NoGo responses at Fz for Go (solid) and NoGo (dashed) conditions across all tasks. The traditional N2 and P3 components, which display a larger amplitude for NoGo than Go responses, can be seen for each condition.

Figure 3

Grand average at Fz across the three inhibition tasks: Single (blue), Multiple (green), and Semantic (red). As can be seen in this depiction there is a decrease in the amplitude of the P3 with task difficulty. A similar trend in the N2.

Figure 4

Grand average of selected electrodes of interest for the Multiple Task: Go (green) NoGo (red). As can be seen in the figure, the inhibitory Go-NoGo effect was largest over the frontal areas.