On average, men pick up on visual motion significantly faster than women do, according to a new study.
Humans’ ability to notice moving objects has always been a useful skill, good for avoiding an animal predator in ancient times and 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. 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.
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—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 “better” 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’s ability to “put the brakes” 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.
“We were very surprised,” says study author Scott Murray, a professor of psychology at the University of Washington. “There is very little evidence for sex differences in low-level visual processing, especially differences as large as those we found in our study.”
Murray and coauthor Duje Tadin of the University of Rochester say that the finding was “entirely serendipitous.” 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’t quite sure where these differences are coming from. So far, the difference between males and females appears to be specific to motion—there were no differences in performance in tasks that involved other types of visual information. The differences aren’t 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’t been recognized, according to the researchers. The results also provide a new window into differences in neural mechanisms that process visual information, Tadin says.
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’t 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 research appears in Current Biology.
The National Institutes of Health funded the research. Additional coauthors are from the University of Washington, the University of Minnesota, the University of Bern in Switzerland; and the University of Witten/Herdecke in Germany.
Source: University of Washington, adapted from a Cell Press release.