Task-induced attention load guides and gates unconscious semantic interference

Abstract

The tight relationship between attention and conscious perception has been extensively researched in the past decades. However, whether attentional modulation extended to unconscious processes remained largely unknown, particularly when it came to abstract and high-level processing. Here we use a double Stroop paradigm to demonstrate that attention load gates unconscious semantic processing. We find that word and color incongruencies between a subliminal prime and a supraliminal target cause slower responses to non-Stroop target words-but only if the task is to name the target word (low-load task), and not if the task is to name the target's color (high-load task). The task load hypothesis is confirmed by showing that the word-induced incongruence effect can be detected in the color-naming task, but only in the late, practiced trials. We further replicate this task-induced attentional modulation phenomenon in separate experiments with colorless words (word-only) and words with semantic relationship but no orthographic similarities (semantics-only).

Fig. 1. Trial sequence, stimulus, and task.

Each trial was self-paced and began with a varied stimulus-onset asynchrony (SOA) ranging from 0.1–1s. After which a dynamic flashing colored Mondrian pattern was presented to the dominant eye while the colored word prime was presented to the non-dominant eye. During 400 ms suppression period, the suppressed word was sandwiched by the Mondrian pattern by two frames at each end, leading to 333 ms presence. The 400-ms-on-400-ms-off pattern was repeated five times or until participants reported breakthrough. If breakthrough was reported, the trial ended immediately. If not, another colored word was presented immediately until response. Participants were instructed to name the word (Experiments 1, 3, and 5, 7) or color (Experiments 2, 4, 6, 8) of the target. A 2-alternative-force-choice location task was present at the end of each trial, participants were instructed to report the location of the suppressed prime. While the prime detection served as a subjective report of prime visibility, this location task served as a post-trial objective gauge of prime visibility. The prime was occasionally superimposed on the Mondrians (visible catch) or simply non-existent (blank catch). Refer to Table 2 for detailed prime-target combinations in all experiments. The prime and target were of different font sizes and presented on slightly jittered locations.

Fig. 2. Experiments 1 and 2 results.

n = 20 in each experiment. Y-axis denotes reaction time, and X-axis denotes congruent and incongruent conditions between the subliminal prime and supraliminal target (CON: congruent; INCON: incongruent; Non-Stroop/Stroop denotes whether target word was a Non-Stroop or Stroop word). A/B, a three- way interaction among word/color congruency and target Stroop, showing double incongruency slowed down responses only when target was not a Stroop word. C~E, reaction time of word congruent and incongruent conditions in all trials (C), 1st quarter trials (D), and the 4th quarter trials (E) in Experiment 2. Black dots and lines denote longer RT in the incongruent condition while gray dots and lines denote longer RT in the congruent condition. Each pair of dots represents one participant. The bars denote group mean with the error bars indicating standard error of the mean (SEM). Asterisk denotes significance (A: Exp 1: p = 0.02 (post hoc 2-tailed paired t test); E: Exp 2 4th quarter trials: p =0.04 (a main effect in a three-way ANOVA)).

Fig. 3. Experiments 3 and 4 results.

n = 20 in each experiment. Y-axis denotes reaction time, and X-axis denotes two critical conditions: word congruent (Word CON) and word incongruent (Word INCON). Black dots and lines denote longer RT in the word incongruent condition while gray dots and lines denote longer RT in the word congruent condition. Each pair of dots represents one participant. The bars denote group mean with the error bars indicating standard error of the mean (SEM). Asterisk denotes significance (A: Exp 3: p = 0.03; D: Exp 4 4th quarter trials: p = 0.02. Both 2-tailed paired t tests).

Fig. 4. Experiments 5 and 6 results.

n = 20 in each experiment. Y-axis denotes reaction time, and X-axis denotes two critical conditions: color congruent (Color CON) and color incongruent (Color INCON). Each pair of dots represents one participant. Black dots and lines denote longer RT in the color incongruent condition while gray dots and lines denote longer RT in the color congruent condition. The bars denote group mean with the error bars indicating standard error of the mean (SEM).

Fig. 5. Experiments 7 and 8 results.

n = 20 in each experiment. Y-axis denotes reaction time, and X-axis denotes two critical conditions: semantically congruent (SEM-CON) and semantically incongruent (SEM-INCON). Black dots and lines denote longer RT in the semantically incongruent condition while gray dots and lines denote longer RT in the semantically congruent condition. Each pair represents one participant. The bars denote group mean with the error bars indicating standard error of the mean (SEM). Asterisk denotes significance (Exp 8, p = 0.02, 2-tailed paired t test from prime-target co-localized trials).