The effects of visual half-field priming on the categorization of familiar intransitive gestures, tool use pantomimes, and meaningless hand movements

Abstract

Although the control of meaningful gestures is one of the most left-lateralized functions, the relative contribution of the two hemispheres to their processing is still debated. We tested the effects of primes appearing in the left or right visual field in the form of pictures (Experiment 1), and words (Experiment 2) on categorization of movies showing intransitive ("communicative") gestures, tool use (transitive) pantomimes, and meaningless movements. Fifteen participants (eight women) watched 36 movies (12 from each category) primed for 150 ms with either a congruent or incongruent stimulus followed by a 50-ms mask. On congruent trials, a picture or word was directly related to the presented gesture, including nonsense pictures or non-words for meaningless actions. On incongruent trials, a picture or word belonged to a different category. In Experiment 1, intransitive gestures were categorized significantly faster than the other two types of hand movements. Moreover, whereas the categorization of transitive gestures was significantly facilitated by congruent pictures on the right, the effect was weaker for intransitive, and reversed for meaningless movements. In Experiment 2, intransitive gestures were again categorized significantly faster, but transitive significantly slower than the other two gesture categories. Yet, there was now a significant facilitation of intransitive, and inhibition of transitive gesture categorization following congruent prime words in the right visual field, and significantly faster categorization of intransitive gestures following incongruent words in the left visual field. These outcomes lend support to the complexity account of differences in left-hemisphere representations of meaningful gestures reported in the neuropsychological, behavioral, and neuroimaging literature. Nevertheless, they also indicate that the representations of intransitive gestures show some differential, and sometimes counterintuitive sensitivity to right hemisphere processing.

Keywords: categorization; intransitive gestures; meaningless actions; pictures; priming; representation; tool use pantomimes; words.

Figure 1

Trial structure and timing. In (A) the priming stimulus was a characteristic hand posture, in (B) it was a picture of a tool, and in (C) an image of a distorted, unrecognizable object. After a fixation point presented on a blank screen for a variable time interval (1000, 1500, or 2000 ms), the priming stimulus was shown either on the left or right (as shown by a grayed inset) for 150 ms, followed by a 50-ms mask, and a centrally presented gesture. The movie stayed on the screen until a participant responded or for up to 4 s. Additional 1-s delay interval was introduced after a movie disappeared.

Figure 2

The main effect of gesture for correctly categorized movies when pictures were used as primes. Intransitive gestures were categorized significantly faster than transitive and meaningless movements. Response times for the latter two did not differ between each other. Asterisks indicate a difference with Bonferroni-corrected p-value of 0.001 (^***).

Figure 3

Response times to correctly categorized intransitive gestures, tool use pantomimes, and meaningless hand movements primed by congruent or incongruent pictorial cues presented in the right or left visual field. Transitive gestures were greatly facilitated by congruent pictorial cues on the right, and intransitive gestures showed a similar trend. The effect for meaningless movements was reversed. Incongruent pictorial cues had no effect on categorization of both meaningful gesture types, but the effect for meaningless movements was in the same direction as before. Asterisks indicate differences with Bonferroni-corrected p-values of at least 0.01 (^**), or 0.001 (^***).

Figure 4

The main effect of gesture for correctly categorized movies when words were used as primes. Intransitive gestures were again categorized significantly faster than transitive and meaningless movements. Response times for the latter two now also differed between each other. Asterisks indicate differences with Bonferroni-corrected p-values of 0.05 (^*), or 0.001 (^***).

Figure 5

Response times to correctly categorized intransitive gestures, tool use pantomimes, and meaningless hand movements primed by congruent or incongruent linguistic cues presented in the right or left visual field. Intransitive gestures were greatly facilitated by congruent linguistic cues on the right, whereas transitive gestures and meaningless movements showed the opposite effect. Incongruent linguistic cues affected the categorization of only intransitive gestures. Asterisks indicate differences with Bonferroni-corrected p-values of at least 0.001 (^***).

Figure 6

The effects of incongruent left-sided cues on intransitive gesture categorization. There are two important comparisons that are considered. As can be predicted, such incongruent cues on the left significantly slowed the categorization of intransitive gestures as compared to congruent cues on the right. Yet, at the same time their negative impact was weaker than that of congruent cues presented on the left. This effect is consistent with an idea that right-hemisphere processing is also important in the categorization of conventionalized intransitive gestures. Asterisks indicate differences with Bonferroni-corrected p-values of at least 0.001 (^***).