From 2018... Those in the low opposite-sex exposure condition rated subsequent individual voices of the opposite sex as significantly more attractive than those who were in the high opposite-sex exposure condition

Hearing Sex at the Cocktail Party: Biased Sex Ratios Influence Vocal Attractiveness. John. G. Neuhoff ORCID Icon &Taylor N. Sikich. Auditory Perception & Cognition, Volume 1, 2018 - Issue 1-2, Sep 25 2018. https://doi.org/10.1080/25742442.2018.1518949

ABSTRACT: Visual exposure to unbalanced sex ratios influences perceived facial attractiveness for opposite-sex faces. When opposite-sex faces are scarce they are rated as more attractive than when they are plentiful. The current work examines a vocal-auditory analog of this effect. Participants were assigned to either a high or low opposite-sex vocal exposure condition and reported summary statistics by estimating the percentage of male and female voices in an array of simultaneous talkers. Participants then rated the attractiveness of individual opposite-sex voices. Those in the low opposite-sex exposure condition rated subsequent individual voices of the opposite sex as significantly more attractive than those who were in the high opposite-sex exposure condition. The findings demonstrate that a core visuo-perceptual aspect of mate selection preference also occurs in the auditory domain. The results are consistent with the idea that the attractiveness of opposite-sex partners is an honest signal of fitness and involves multimodal processes that are quickly modulated by the perceived availability of opposite-sex partners in a local environment.

KEYWORDS: Sex ratio, ensemble coding, summary statistics, vocal attractiveness, mate selection

Discussion

Simultaneously sounding voices have historically been treated as “background” stimuli in auditory perception research (Brungart & Simpson, 2007; Brungart, Simpson, Ericson, & Scott, 2001; Cox, Alexander, & Rivera, 1991; Darwin, 2008). However, the current results confirm that when directed to attend to multiple simultaneous voices, listeners can use ensemble coding to extract summary statistics and scale the percentage of male and female voices in the array (Neuhoff, 2017). Moreover, when listeners hear a low percentage of opposite-sex voices, subsequent individual opposite sex voices are perceived as more attractive than when they hear a high percentage of opposite-sex voices.

Sex Ratios and Vocal Attractiveness
The effect of unbalanced sex ratios on perceived attractiveness is consistent with previous work that examines the relationship between sex ratios and mate selection behavior. Favorable sex ratios (a larger choice of potential opposite-sex mates and fewer same-sex rivals) are associated with choosier mate selection behaviors and raised standards of attractiveness in a potential mate (Hahn et al., 2014; Munro et al., 2014; Watkins et al., 2012). From a theoretical perspective, modulating mate selection preferences and behaviors based on the perception of unbalanced sex ratios makes evolutionary sense. Sociosexual behaviors in populations with biased sex ratios skew toward the preferences of the minority sex, which can be more selective because they face less competition from same-sex rivals (Moss & Maner, 2016; Pedersen, 1991; Pollet & Nettle, 2008; Schmitt, 2005). Lowering attractiveness standards in the face of unfavorable sex ratios is a behavior that expands the pool of potential mates (Watkins et al., 2012). The current findings for unbalanced vocal sex ratios are consistent with research on sex ratios and facial attractiveness and provide converging support for a reliable relationship between vocal and visual attractiveness (Abend et al. 2015; Puts et al., 2016).

This suggests that observers use multimodal sources of information when evaluating potential opposite-sex partners and that the process may involve a high degree of automaticity. For example, Mileva, Tompkinson, Watt, and Burton (2018) showed that impression formation involves a mandatory and immediate integration of both vocal and facial information. Future work might examine the degree to which the perception of summary statistics from voices and the effects of unbalanced sex ratios on attractiveness involve automatic processes. In the current work, listeners accurately scaled sex ratios after exposures of only 1500 ms and showed effects of unbalanced sex ratios on perceived attractiveness after cumulative exposure of only 1.2 min (48 trials × 1500 ms). We also found a main effect for the number of voices presented in the exposure phase. Listeners presented with 5 simultaneous voices perceived subsequent individual voices to be more attractive than those first presented with 10 simultaneous voices. Although we did not specifically ask our participants to report the number of voices in the exposure stimuli, the results are consistent with the overarching hypothesis that standards of attractiveness will be lowered (i.e., voices will be rated as more attractive) when the number of potential opposite-sex partners is diminished.

Finally, we found a main effect for participant sex that indicated men found female voices more attractive than women found male voices. This finding could simply be a function of the relative attractiveness between male and female voices in our study.

Ericson, & Scott, 2001; Cox, Alexander, & Rivera, 1991; Darwin, 2008). However, the current results confirm that when directed to attend to multiple simultaneous voices, listeners can use ensemble coding to extract summary statistics and scale the percentage of male and female voices in the array (Neuhoff, 2017). Moreover, when listeners hear a low percentage of opposite-sex voices, subsequent individual opposite sex voices are perceived as more attractive than when they hear a high percentage of opposite-sex voices. Sex Ratios and Vocal Attractiveness The effect of unbalanced sex ratios on perceived attractiveness is consistent with previous work that examines the relationship between sex ratios and mate selection behavior. Favorable sex ratios (a larger choice of potential opposite-sex mates and fewer same-sex rivals) are associated with choosier mate selection behaviors and raised standards of attractiveness in a potential mate (Hahn et al., 2014; Munro et al., 2014; Watkins et al., 2012). From a theoretical perspective, modulating mate selection preferences and behaviors based on the perception of unbalanced sex ratios makes evolutionary sense. Sociosexual behaviors in populations with biased sex ratios skew toward the preferences of the minority sex, which can be more selective because they face less competition from same-sex rivals (Moss & Maner, 2016; Pedersen, 1991; Pollet & Nettle, 2008; Schmitt, 2005). Lowering attractiveness standards in the face of unfavorable sex ratios is a behavior that expands the pool of potential mates (Watkins et al., 2012).

The current findings for unbalanced vocal sex ratios are consistent with research on sex ratios and facial attractiveness and provide converging support for a reliable relationship between vocal and visual attractiveness (Abend et al. 2015; Puts et al., 2016). This suggests that observers use multimodal sources of information when evaluating potential opposite-sex partners and that the process may involve a high degree of automaticity. For example, Mileva, Tompkinson, Watt, and Burton (2018) showed that impression formation involves a mandatory and immediate integration of both vocal and facial information. Future work might examine the degree to which the perception of summary statistics from voices and the effects of unbalanced sex ratios on attractiveness involve automatic processes. In the current work, listeners accurately scaled sex ratios after exposures of only 1500 ms and showed effects of unbalanced sex ratios on perceived attractiveness after cumulative exposure of only 1.2 min (48 trials × 1500 ms). We also found a main effect for the number of voices presented in the exposure phase. Listeners presented with 5 simultaneous voices perceived subsequent individual voices to be more attractive than those first presented with 10 simultaneous voices. Although we did not specifically ask our participants to report the number of voices in the exposure stimuli, the results are consistent with the overarching hypothesis that standards of attractiveness will be lowered (i.e., voices will be rated as more attractive) when the number of potential opposite-sex partners is diminished.

Finally, we found a main effect for participant sex that indicated men found female voices more attractive than women found male voices. This finding could simply be a function of the relative attractiveness between male and female voices in our study. However, it is also a finding that occurs consistently when men and women are asked to give opposite-sex attractiveness ratings (Gladue & Delaney, 1990; Hahn et al., 2014; Johnco et al., 2010) and is consistent with a higher priority in men than in women for physical attractiveness as an important criterion for mate selection (Boxer et al., 2015; Buss, 1989; Buss & Barnes, 1986).

Effect Sizes
We found very large effects sizes between conditions when listeners were asked to judge the percentage of males and females in our multiple voice exposure stimuli. The effect size for the linear trend for perceived sex ratio as a function of actual sex ratio was ηp 2 = .42 (equivalent to Cohen’s d = 1.7). Neuhoff (2017) also found large effect sizes when participants were asked to scale vocal sex ratios that ranged from 0% to 100%. The size of the effect speaks to the robust ability of listeners to scale sex ratios of multiple simultaneous voices.

However, even effect sizes this large likely underestimate the true effect size that might occur in more natural environments. Under natural listening conditions, multiple simultaneous talkers emanate from separate locations in space (rather than centrally from headphones or loudspeakers). Spatial separation of talkers reduces auditory cognitive load and affords a better assessment of target speech among multiple talkers (Andeol, Suied, Scannella, & Dehais, 2017; Bronkhorst, 2000; Shinn-Cunningham, Ihlefeld, Satyavarta, & Larson, 2005). Thus, spatial separation might also afford more accurate estimates of sex ratios. In a similar light, it may also be the case that durations of exposure to multiple voices longer than 1500 ms would provide a better assessment of vocal sex ratios.

In contrast to the large effect sizes for scaling sex ratios, the effect size for the difference in attractiveness ratings between high and low opposite sex exposure conditions was comparatively small (ηp 2 = .02, equivalent to Cohen’s d = .29). Our design had sufficient power to detect this effect size, and it may be that the factors of increased spatial separation and stimulus duration that would occur in a natural environment would also increase the effects of unbalanced sex ratios on attractiveness. The fact that exposure and attractiveness ratings occurred in temporally separate blocks may also contribute to the smaller observed effect size.

However, effect sizes need not be large to be important from an evolutionary perspective. On the contrary, small but reliable effect sizes can be instrumental in explaining how our evolutionary history shaped current perceptual and cognitive abilities (Voyer, Voyer, & Bryden, 1995; Weiss, Kemmler, Deisenhammer, Fleischhacker, & Delazer, 2003; Zilles et al., 2016). For example, in evolutionary psychology, finding sex differences can be critically important evidence that supports a behavioral adaptation. Yet, a meta-analysis of 286 studies on sex differences in spatial perception showed a mean effect size of only d = .37 (ηp 2 = .03; Voyer et al., 1995). Although such small effect sizes are not helpful in predicting the behavior of any particular individual based on sex, they are indicative of differential challenges faced by men and women over the course of evolutionary history. The effect size in our results is also similar to that found for the effect of biased sex ratios on facial attractiveness (ηp 2 = .02, Hahn et al., 2014).

Limitations and Future Research
Our sample included only heterosexual participants. Thus, it is an open question as to how exposure to unbalanced sex ratios might influence participants of other sexual orientations or how participant sexual orientation might interact with the orientation of the to-be-judged talker. Although our results do not speak to these questions, there is considerable evidence to suggest that sexual orientation is likely an important factor in these kinds of investigations and could be a fruitful avenue for further research (Hancock & Pool, 2017; Munson, 2007; Rule, 2017; Valentova, Roberts, & Havlicek, 2013).

The online nature of our data collection introduced variability that might not have been present under more controlled laboratory conditions. For example, participants listened to the stimuli as compressed mp3 files on their own devices at different levels with varying amounts of background noise in each unique listening environment. Nonetheless, all these factors introduce variability that makes it less likely to reject the null hypothesis. Finding significant results in the face of this increased variability speaks to the robust nature of the effects and increases the external validity of the findings.

Online data collection also resulted in a more diverse sample than what we would expect to obtain in typical undergraduate samples. While this is a desirable characteristic of samples, the mean age of our participants (39 years) was considerably older than that of the talkers whose voices were rated for attractiveness (20 years). Although this poses no threat to internal validity (all participants rated voices of the same age), it would be interesting to examine how participant and talker age interact in future studies of sex ratios and attractiveness.