Forest Before Trees: Letter Stimulus and Sex Modulate Global Precedence in Visual Perception

Abstract

The global precedence effect (GPE), originally referring to processing hierarchical visual stimuli composed of letters, is characterised by both global advantage and global interference. We present herein a study of how this effect is modulated by the variables letter and sex. The Navon task, using the letters "H" and "S," was administered to 78 males and 168 females (69 follicular women, 52 luteal women, and 47 hormonal contraceptive users). No interaction occurred between the letter and sex variables, but significant main effects arose from each of these. Reaction times (RTs) revealed that the letter "H" was identified more rapidly in the congruent condition both in the global and the local task, and the letter "S" in the incongruent condition for the local task. Also, although RTs showed a GPE in both males and females, males displayed shorter reaction times in both global and local tasks. Furthermore, luteal women showed higher d' index (discrimination sensitivity) in the congruent condition for the local task than both follicular women and hormonal contraceptive users, as well as longer exploration time of the irrelevant level during the global task than males. We conclude that, according to the linear periodicity law, the GPE is enhanced for compound letters with straight vs. curved strokes, whereas it is stronger in males than in females. Relevantly, luteal phase of the menstrual cycle seems to tilt women to rely on finer grained information, thus exhibiting an analytical processing style in global/local visual processing.

Keywords: Navon task; global precedence; global/local processing; hierarchical figures; menstrual cycle; sex differences; visual attention; visual perception.

FIGURE 1

Stimuli used: (A) congruent condition; (B) incongruent condition; (C) control stimuli for the global task; (D) control stimuli for the local task. Note the different letter-form (straight vs. curved strokes in the letters “H” and “S,” respectively) and the different number of elements in each large letter (12 elements in the letter “H” and 14 in the letter “S”).

FIGURE 2

Results of pairwise comparisons of RTs for the factors Task × Congruency × Letter. Task: global, local; target Letter: “H”, “S”; stimulus Congruency: congruent, incongruent, control; ^∗statistically significant differences (p < 0.05). Error bars show standard error of the mean. Note that the letter “H” was associated with shorter RTs in both tasks for the control and congruent conditions. In the incongruent condition, no differences were found between these two letters in the global task, while in the local task the letter “S” obtained shorter RTs.

FIGURE 3

Results of pairwise comparisons of RTs for the factors Task× Congruency× Sex. Task: global, local; Sex: males, females; stimulus Congruency: congruent, incongruent, control. *Statistically significant differences (p < 0.05). Error bars show standard error of the mean. Note that men exhibited shorter RTs than women in all tasks and conditions.

FIGURE 4

Results of pairwise comparisons of RTs for the factors Task × Congruency × Hormonal status. Stimulus Congruency: congruent, incongruent, control; Hormonal status: males, follicular women, luteal women, hormonal contraceptive users; Task: global, local. *Statistically significant differences (p < 0.05). Error bars show standard error of the mean.

FIGURE 5

Results of pairwise comparisons of d’ index for the factors Task × Congruency × Hormonal status. Stimulus Congruency: congruent, incongruent; Hormonal status: males, follicular women, luteal women, hormonal contraceptive users; Task: global, local. *Statistically significant differences (p < 0.05). Error bars show standard error of the mean. Note that significant differences according to the Hormonal status were only observed in the congruent condition for the local task.