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. 2015 Apr 1;35(13):5351-9.
doi: 10.1523/JNEUROSCI.1152-14.2015.

Improvement in Visual Search With Practice: Mapping Learning-Related Changes in Neurocognitive Stages of Processing

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Free PMC article

Improvement in Visual Search With Practice: Mapping Learning-Related Changes in Neurocognitive Stages of Processing

Kait Clark et al. J Neurosci. .
Free PMC article

Abstract

Practice can improve performance on visual search tasks; the neural mechanisms underlying such improvements, however, are not clear. Response time typically shortens with practice, but which components of the stimulus-response processing chain facilitate this behavioral change? Improved search performance could result from enhancements in various cognitive processing stages, including (1) sensory processing, (2) attentional allocation, (3) target discrimination, (4) motor-response preparation, and/or (5) response execution. We measured event-related potentials (ERPs) as human participants completed a five-day visual-search protocol in which they reported the orientation of a color popout target within an array of ellipses. We assessed changes in behavioral performance and in ERP components associated with various stages of processing. After practice, response time decreased in all participants (while accuracy remained consistent), and electrophysiological measures revealed modulation of several ERP components. First, amplitudes of the early sensory-evoked N1 component at 150 ms increased bilaterally, indicating enhanced visual sensory processing of the array. Second, the negative-polarity posterior-contralateral component (N2pc, 170-250 ms) was earlier and larger, demonstrating enhanced attentional orienting. Third, the amplitude of the sustained posterior contralateral negativity component (SPCN, 300-400 ms) decreased, indicating facilitated target discrimination. Finally, faster motor-response preparation and execution were observed after practice, as indicated by latency changes in both the stimulus-locked and response-locked lateralized readiness potentials (LRPs). These electrophysiological results delineate the functional plasticity in key mechanisms underlying visual search with high temporal resolution and illustrate how practice influences various cognitive and neural processing stages leading to enhanced behavioral performance.

Keywords: EEG; LRP; N2pc; attention; learning; visual search.

Figures

Figure 1.
Figure 1.
Hypothetical model indicating potential changes in behavior and ERP components in a visual search task after practice. A, Response time (RT) is expected to decrease after practice. B, Horizontal arrows indicate potential latency shifts in the N1, N2pc, and LRP components. Vertical arrows indicate potential amplitude changes in the P1/N1, N2pc, and SPCN components.
Figure 2.
Figure 2.
Sample stimulus display. The blue ellipses were distractors, the green ellipse was the relevant color popout target, and the red ellipse was the irrelevant color popout nontarget. Participants responded as to the orientation of the green target ellipse. In this example, a participant would respond by pressing the button corresponding to “horizontal.”
Figure 3.
Figure 3.
Behavioral results. The response time (A) and accuracy values (B) are shown across the sessions. The response time decreased significantly over the course of practice, but there was no significant change in accuracy.
Figure 4.
Figure 4.
Effects on the N1 sensory component. A, ERP traces of the sensory-evoked N1 component, collapsed across targets on the left and right sides of the display, demonstrating an overall bilateral increase in amplitude after practice. B, Distribution of N1-related activity over the scalp in response to the search arrays.
Figure 5.
Figure 5.
Effects on the N2pc and SPCN lateralized components, reflecting attentional orienting and target discrimination difficulty, respectively. A, ERP traces of activity used to calculate the difference waves for deriving the N2pc and SPCN components (contralateral vs ipsilateral to the target popout). B, Difference waves displaying N2pc and SPCN components in the posterior parietal–occipital regions of interest. C, Distribution of N2pc-related activity over the scalp for Sessions 1 and 5. D, Distribution of SPCN-related activity over the scalp for Sessions 1 and 5.
Figure 6.
Figure 6.
Effects on the LRP component, reflecting stimulus-locked motor preparation activity and response-locked motor preparation activity. A, ERP traces of activity used to calculate contralateral versus ipsilateral difference waves used for deriving the LRP component (contralateral vs ipsilateral to the hand used for the motor response), time-locked to the onset of the stimulus array (stimulus-locked, left traces) and to the response time (response-locked, right traces). B, Difference waves displaying the LRP component. C, Distribution of LRP-related activity over the scalp for Sessions 1 and 5.

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