Exploring the Limitations of the Shielding Function of Categorization Rules in Task-Switching

Abstract

Applying categorization rules narrows attention toward the relevant features of a target and helps participants to ignore the irrelevant features of the target. This is called the shielding function of categorization rules. Here we explored the limitation of the shielding function in two task-switching experiments. In Experiment 1, we assigned each target a single digital numeral as an additional feature in addition to conventional bivalent features as in the previous task-switching experiments with bivalent tasks. In the first two stages of Experiment 1, half of the participants learned the numeral-response associations and the other half used an alternative numeral-categorization rule to infer the response. Without participants applying conventional task-switching rules, the switching costs disappeared. Moreover, when participants performed tasks by numeral-response associations the bivalent features interfered with response retrieval and caused response-congruency effects, whereas when participants applied the numeral-categorization rule, the bivalent features were shielded away and thereby the response-congruency effects disappeared. In the third stage, in which all participants applied task-switching rules by discriminating between bivalent features (i.e., filling and orientations), we found task-switching costs and response-congruency effects. In Experiment 2, new bivalent features produced stronger interference compared to Experiment 1. As a consequence, participants in both the association group and the numeral-categorization rule group showed significant response-congruency effects in the first two stages, where task-switching rules were not introduced. It follows that the shielding function of categorization rules has limits-strong interference from bivalent features can break down the shielding function. In addition, participants in the association group showed task-switching costs without being informed about the task-switching rules. We propose that strong proactive interference can produce task-switching costs even without the use of task-switching rules.

Keywords: bivalent features; congruency effect; shielding function of task set; task-switching; task-switching cost.

FIGURE 1

Illustration of cues, target stimuli, and response rules in Experiment 1. (A) Task cues and examples of bivalent features that participants needed to attend to in the filling task and orientation task. (B) Target stimuli and the response for the association group. Each target stimulus consisted of a single digital numeral presented centrally and a vertically or horizontally oriented rectangle bar either with or without filling. The digits for the congruent/incongruent target stimuli were counterbalanced between Target Set One and Target Set Two, giving a total of sixteen target stimuli for each participant. Digits 2, 5, 7, and 8 were always associated with the left key and digits 1, 3, 4, and 6 were always associated with the right key regardless of the bivalent features. (C) Target stimuli and the response for the numeral-categorization group. Participants should press the left key to respond to an odd number and the right key to respond to an even number, regardless of the bivalent features.

FIGURE 2

Results of Experiment 1. (A) The violin plots illustrate RT distributions for all 48 participants (24 participants from the association group and 24 participants from the numeral-categorization group) in repeat and switch trials and each stage (Stage 1, Stage 2, and Stage 3). Jittered dots represent individual average RTs. The black horizontal bar and the box represent the mean and 50% CI of the mean in each condition. (B) Violin plots illustrate RT distributions of congruent and incongruent trials for each stage in the association group. (C) Violin plots illustrate RT distributions of congruent and incongruent trials for each stage in the numeral-categorization group. ^∗∗∗p < 0.001; ^∗∗p < 0.05; and ns = non-significant.

FIGURE 3

Illustration of cues, target stimuli, and the corresponding responses in Experiment 2. (A) Task cues and examples of the arrow features of target stimuli. (B) Target stimuli for the association group. Each target stimulus consisted of two arrows. Digits 2, 5, 7, and 8 were always associated with the left key and digits 1, 3, 4, and 6 were always associated with the right key. (C) Target stimuli for the numeral-categorization group. Participants should press the left key to respond to an odd number and the right key to respond to an even number. (D) An example of cue-target combination. A single digital numeral was always presented in the center.

FIGURE 4

Results of Experiment 2. (A) The violin plots illustrate RT distributions for participants in the numeral-response association group for repeat and switch trials across stages (Stage 1, Stage 2, and Stage 3). Jittered dots represent individual average RTs. The black horizontal bar and the box represent the mean and 50% CI of the mean in each condition. (B) The violin plots illustrate RT distributions for participants in the numeral-categorization group for repeat and switch trials across stage. (C) The violin plots illustrate RT distributions for participants in the association group for the congruent and incongruent trials and each stage. (D) The violin plots illustrate RT distributions for participants in the numeral-categorization group for the congruent and incongruent trials across stages. ^∗∗∗p < 0.001; ^∗∗p < 0.05; and ns = non-significant.