Humans鈥� ability to notice moving objects has always been a useful skill, from avoiding an animal predator in ancient times to crossing a busy street in the modern world.
That evolutionary success attests to the importance of visual motion processing, and why there may be specialized regions of the brain specifically dedicated to this function, researchers say. 聽To shed light on how neurons respond in these regions, researchers can look for small differences in motion perception among groups of people.
One of those perceptual differences may be between the sexes.
In an published Aug. 16 in Current Biology, a 天美影视传媒-led team of researchers says that on average, men pick up on visual motion significantly faster than women do.
The study, which involved more than 250 adult men and women, shows that both males and females are good at reporting whether black and white bars on a screen are moving to the left or to the right 鈥� requiring only a tenth of a second and often much less to make the right call. But, compared to men, women regularly took about 25 to 75 percent longer.
The researchers say that the faster perception of motion by males may not necessarily reflect 鈥渂etter鈥� visual processing. They note that faster motion processing has been observed in individuals diagnosed with autism spectrum disorder (ASD), depression, and in older individuals. All three of these conditions have been linked to disruptions in the brain鈥檚 ability to 鈥減ut the brakes鈥� on neural activity. The authors speculate that this regulatory process may also be weaker in the male brain, allowing males to process visual motion faster than females.
鈥淲e were very surprised,鈥� UW psychology professor said. 鈥淭here is very little evidence for sex differences in low-level visual processing, especially differences as large as those we found in our study.鈥�
Murray and co-author Duje Tadin of the University of Rochester say that the finding was 鈥渆ntirely serendipitous.鈥� They were using the visual motion task to study processing differences in individuals with ASD. Because boys are about four times more likely to be diagnosed with ASD than girls, the researchers included sex as a factor in their analysis of the control group, the members of which did not have ASD. The sex difference in visual perception of motion became immediately apparent.
To confirm the findings, the researchers asked other investigators who had used the same task in their own experiments for additional data representing larger numbers of study participants. And those independent data showed the same sex difference pattern.
The researchers aren鈥檛 quite sure where these differences are coming from. So far, the difference between males and females appears to be specific to motion 鈥� there were no differences in performance in tasks that involved other types of visual information. The differences aren鈥檛 apparent in functional MRI scans of the brain, either.
Overall, according to the study, the results show how sex differences can manifest unexpectedly. The results also highlight the importance of considering sex as a potential factor in any study of perception or cognition.
These findings come as evidence that visual processing differs in males and females in ways that hadn鈥檛 been recognized, according to the researchers. The results also provide a new window into differences in neural mechanisms that process visual information, Tadin said.
In further studies, the researchers hope to discover the underlying differences in the brain that may explain this discrepancy in visual motion processing between males and females. Because brain images of the key motion-processing areas haven鈥檛 offered up any clues, the difference may originate in other portions of the brain or may be difficult to measure using current techniques. Ultimately, researchers say, this research might even yield new clues for understanding a vexing question: why ASD is more common in males.
The study was funded by the National Institutes of Health. Other co-authors were , a professor in the UW Department of Psychiatry & Behavioral Sciences; postdoctoral researcher Tamar Kolodny, former postdoctoral researcher Rachel Millin and former research assistant Alex Kale, all in the UW Department of Psychology; Michael-Paul Schallmo of the University of Minnesota; Philipp Thomas and Thomas Rammsayer of the University of Bern, in Switzerland; and Stefan Troche of the University of Witten/Herdecke, in Germany.
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For more information, contact Murray at somurray@uw.edu or Tadin at dtadin@ur.rochester.edu.
Adapted from a release by Cell Press.