ERP characterization of sustained attention effects in visual lexical categorization

Abstract

As our understanding of the basic processes underlying reading is growing, the key role played by attention in this process becomes evident. Two research topics are of particular interest in this domain: (1) it is still undetermined whether sustained attention affects lexical decision tasks; (2) the influence of attention on early visual processing (i.e., before orthographic or lexico-semantic processing stages) remains largely under-specified. Here we investigated early perceptual modulations by sustained attention using an ERP paradigm adapted from Thierry et al. [1]. Participants had to decide whether visual stimuli presented in pairs pertained to a pre-specified category (lexical categorization focus on word or pseudoword pairs). Depending on the lexical category of the first item of a pair, participants either needed to fully process the second item (hold condition) or could release their attention and make a decision without full processing of the second item (release condition). The P1 peak was unaffected by sustained attention. The N1 was delayed and reduced after the second item of a pair when participants released their attention. Release of sustained attention also reduced a P3 wave elicited by the first item of a pair and abolished the P3 wave elicited by the second. Our results are consistent with differential effects of sustained attention on early processing stages and working memory. Sustained attention modulated early processing stages during a lexical decision task without inhibiting the process of stimulus integration. On the contrary, working memory involvement/updating was highly dependent upon the allocation of sustained attention. Moreover, the influence of sustained attention on both early and late cognitive processes was independent of lexical categorization focus.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Behavioral results.

W refers to Words, P to pseudowords (lexical category under focus), H to Hold and R to Release (sustained attention). Mean reaction times are depicted by histograms and mean error rates are depicted by circles. Error bars indicate standard errors. The reference time for reaction time values is the onset of the stimulus of the pair which has induced the participant's answer, i.e. the onset of the first stimulus of the pair in the ‘release’ condition and the onset of the second stimulus in the ‘hold’ condition.

Figure 2. ERP results, general overview.

Event-related potential results over nine major scalp regions (Left Frontal, electrodes F3, F5, FC3, FC5, FT7; FrontoCentral, F1, F2, FC1, FCz, FC2; Right Frontal, F4, F6, FC4, FC6, FT8; Left Temporal, C3, C5, CP3, CP5, TP7; ParietoCentral, C1, Cz, C2, CP1, CP2; Right Temporal, C4, C6, CP4, CP6, TP8; Left ParietoOccipital, P3, P5, PO3, PO7, O1; ParietoOccipital, P1, Pz, P2, POz, Oz; Right ParietoOccipital, P4, P6, PO4, PO8, O2). a. Lexical categorization focus on word pairs. b. Lexical categorization focus on pseudoword pairs. ERPs for hold (full line) and release (dotted line) sustained attention conditions. Vertical bars on graphs indicate the onset of the first and second item of a pair.

Figure 3. Event-related potential results for the first item of a pair.

ERPs measured over parietooccipital region (PO3, PO4, O1, O2, P5, P6, PO7, PO8) for lexical categorization focus and sustained attention conditions (W-hold = words under focus, hold condition; W-release = words under focus, release condition; P-hold = pseudowords under focus, hold condition; P-release = pseudowords under focus, release condition). Rectangles on the time axis indicate the onset and duration of the first and second item of each pair. Vertical bars indicate reaction times.

Figure 4. Event-related potential results for the first item of a pair.

ERPs measured over centroparietal region (C1, C2, Cz, CP1, CP2, CPz, P1, P2) for lexical categorization focus and sustained attention conditions. Rectangles on the time axis indicate the onset and duration of the first and second item of each pair. Vertical bars indicate reaction times. Topographies labelled with stars are significantly different.

Figure 5. Event-related potential results elicited by the second item of a pair.

ERPs measured over parietooccipital region (PO3, PO4, O1, O2, P5, P6, PO7, PO8) for lexical categorization focus and sustained attention conditions. Rectangles on the time axis indicate the onset time and duration of the first and second item of each pair. Vertical bars indicate reaction times. Topographies labelled with stars are significantly different. Time scale and ERP baseline correction were recalculated in reference to the onset of the second item.

Figure 6. Event-related potential results for the second item of a pair.

ERPs measured over centroparietal region (C1, C2, Cz, CP1, CP2, CPz, P1, P2) for lexical categorization focus and sustained attention conditions. Rectangles on the time axis indicate the onset time and duration of the first and second item of each pair. Vertical bars indicate reaction times. Topographies labelled with stars are significantly different. Time scale and ERP baseline correction were recalculated in reference to the onset of the second item.

Figure 7. ERP results, summary.

Mean amplitudes, mean latencies and standard errors associated with each ERP event in the four experimental conditions (Lexical categorization focus on words or pseudowords; Hold or released sustained attention).

Figure 8. Experimental design: Example of one trial.