Hands as sex cues: sensitivity measures, male bias measures, and implications for sex perception mechanisms

Abstract

Sex perceptions, or more particularly, sex discriminations and sex categorisations, are high-value social behaviours. They mediate almost all inter-personal interactions. The two experiments reported here had the aim of exploring some of the basic characteristics of the processes giving rise to sex perceptions. Experiment 1 confirmed that human hands can be used as a cue to an individual's sex even when colour and texture cues are removed and presentations are brief. Experiment 1 also showed that when hands are sexually ambiguous observers tend to classify them as male more often than female. Experiment 2 showed that "male bias" arises not from sensitivity differences but from differences in response biases. Observers are conservative in their judgements of targets as female but liberal in their judgements of targets as male. These data, combined with earlier reports, suggest the existence of a sex-perception space that is cue-invariant.

Figure 1. Stimulus exemplars used in these experiments.

Hand stimuli were standardised for absolute size via a process of reduction (depicted) and enlargement. Within each stimulus condition 15 female and 15 male exemplars were represented. Each reduced and enlarged image had an absolute pixel count of 44,693 px and 89,394 px respectively (±10%).

Figure 2. Sex classification error rates.

Group proportions of sex classification errors in response to female (a) and male (b) hand images presented for 125 ms and for 1000 ms. Performances are shown for hands with colour/texture cues (open circles) and without (silhouettes: filled circles). Vertical bars represent ±1 SEM. Chance performance is represented by the dashed line. Performances above that line represent a systematic tendency to misreport stimulus sex.

Figure 3. Sex classification sensitivity for ambiguous silhouette hands.

Standardised group sensitivity (d′) scores, representing the ability to distinguish target from lure trials, as a function both of target sex (female and male) and whether hands were presented for 125 ms (open circles) or 1000 ms (filled circles). Data corresponding to silhouette hand stimuli conditions are depicted, although observers were also presented colour hands. Vertical bars represent ±1 SEM.

Figure 4. Sex classification bias.

Standardised group criterion (c) scores, representing the tendency to respond ‘target absent’ (c>0) or ‘target present’ (c<0), as a function both of target sex (female and male) and presentation duration (125 ms: open circles; 1000 ms: filled circles). The insert shows the absolute mean bias score for both female and for male targets. Observers were generally male biased at both 125 ms (c _diff = 0.81±0.28) and 1000 ms (c _diff = −0.48±0.24) presentation durations. One-sample t tests indicated that the absolute mean bias was significant at the shorter (t ₁₀ = 2.92, p = .015), but not the longer (t ₁₀ = 1.99, p = .075) exposure time. Vertical bars represent ±1 SEM.