Oxytocin in Motion

 

Oxytocin, sometimes referred to as the “love hormone,” is known for its role in facilitating social interactions; it fosters mother-child bonding (West, 2007), improves social cognition (Association for Psychological Science [APS], 2010a), and stimulates trust (APS, 2010b), among others.

To further examine the function of oxytocin in human social cognitive and emotional processes, Kéri & Benedek (2009) investigated on the effect of externally administered oxytocin on the visual perception of social and nonsocial stimuli. The researchers devised a 2 x 2 x 2 within-subjects experimental design (stimulus type [biological/nonbiological] vs. difficulty [number of mask dots] vs. test condition [oxytocin/placebo]) to test the hypothesis that oxytocin improves the perception of biological motion but has no effect on the detection of structured nonbiological motion.

Kéri & Benedek (2009) adapted the stimuli used by Hiris (2007). A treadmill walking pattern was used to represent the biological motion, while a structured rotation target was used for the nonbiological motion. Each stimulus was consisted of eleven white dots on a black background. These were embedded among clouds of either 176 or 352 dynamic mask dots randomly placed on the stimulus area.

Figure 1. Illustration of the stimuli used for the assessment of biological and nonbiological motion perception. The walking character performed a treadmill-like motion, whereas the square was rotating (see also the online movies available at http://journalofvision.org/7/12/4/images/
Movie1.mov and http://journalofvision.org/7/12/4/
images/Movie3.mov [Hiris, 2007]). The signal dots are marked by arrows (Keri & Benedek, 2009).

The twenty participants had to determine whether the target stimulus was present within the mask dots or not. They had to go through 100 trials for each condition, adding up to a total of 400 trials. Forty-five minutes before the beginning of the experiment, the participants were intranasally given a single dose of 24 IU oxytocin spray or placebo. Each of them underwent the oxytocin and the placebo conditions with a one-week interval.

Figure 2. Sensitivity (d’) values for biological and nonbiological motion after intranasal administration of oxytocin and placebo. Data are means. Error bars indicate 95% confidence intervals. *p < .05, Scheffé’s tests (Keri & Benedek, 2009).

Results have shown that oxytocin enhances the perception of biological motion by increasing sensitivity for stimuli that represent living objects, but does not change the sensitivity for nonbiological stimuli. What the researchers have accomplished is to provide further support to the claim that oxytocin is, indeed, involved in the facilitation of social processes. Through their experiment, however, they have achieved to do so on a more basic level, and that is to show the involvement of oxytocin in motion perception of biologically and socially relevant actors.

References:

Association for Psychological Science. (2010a). Hormone oxytocin improves social cognition but only in less socially proficient individuals. Retrieved from http://www.psychologicalscience.org/index.php/news/releases/hormone-oxytocin-improves-social-cognition-but-only-in-less-socially-proficient-individuals.html

Association for Psychological Science.(2010b). Study suggests oxytocin makes people trusting, but not gullible. Retrieved from http://www.psychologicalscience.org/index.php/news/releases/study-suggests-oxytocin-makes-people-trusting-but-not-gullible.html

Hiris, E. (2007). Detection of biological and nonbiological motion. Journal of Vision, 7(12), 1-16.

Kéri, S., & Benedek, G. (2009). Oxytocin enhances the perception of biological motion in humans. Cognitive, Affective & Behavioral Neuroscience, 9(3), 237-241. doi:10.3758/CABN.9.3.237

West, C. (2007). Level of oxytocin in pregnant women predicts mother-child bond. Observer, 20(10). Retrieved from http://www.psychologicalscience.org/index.php/publications/observer/2007/november-07/level-of-oxytocin-in-pregnant-women-predicts-mother-child-bond-2.html

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