Evidence of Serial Processing in Visual Word Recognition

Abstract

To test the limits of parallel processing in vision, we investigated whether people can recognize two words at once. Participants viewed brief, masked pairs of words and were instructed in advance to judge both of the words (dual-task condition) or just one of the words (single-task condition). For judgments of semantic category, the dual-task deficit was so large that it supported all-or-none serial processing: Participants could recognize only one word and had to guess about the other. Moreover, participants were more likely to be correct about one word if they were incorrect about the other, which also supports a serial-processing model. In contrast, judgments of text color with identical stimuli were consistent with unlimited-capacity parallel processing. Thus, under these conditions, serial processing is necessary to judge the meaning of words but not their physical features. Understanding the implications of this result for natural reading will require further investigation.

Keywords: divided attention; language; open data; visual attention; visual perception; word recognition.

Fig. 1.

Example dual-task semantic trials of Experiments 1 (a) and 2 (b). In Experiment 1, the rapid-serial-visual-presentation (RSVP) rate was adjusted for each participant (see the text). Not shown in panel (a) are the interstimulus intervals (ISIs) between each frame, during which only the fixation cross was presented. In Experiment 2, the duration of the two ISIs between masks and words was adjusted for each participant. The category name (“anatomy”) was actually presented below fixation. In these examples, the postcue is the blue line that points to the side to be judged, but for half of the participants, it was the green line. Dual-task trials are shown here; in single-task trials, there was only one postcue, as the participant had to judge only one side.

Fig. 2.

Attention operating characteristics (AOCs) for semantic judgments (left column) and color judgments (right column) in Experiments 1 (top row) and 2 (bottom row). Solid points pinned to the axes are single-task accuracy levels (A_g); open points are dual-task accuracy levels. Error bars show ±1 SEM.

Fig. 3.

Dual-task accuracy (A_g) when the response to the other side was incorrect plotted against accuracy when the response to the other side was correct, separately for (a) Experiment 1 and (b) Experiment 2. Each point is 1 participant’s data for one judgment type. Points below the unity line indicate that accuracy was better when the other side’s response was incorrect.