LA JOLLA, CA - It doesn't take John Wayne's deliberate, pigeon-toed swagger or Marilyn Monroe's famously wiggly sway to judge a person's gender based on the way they move. People are astonishingly accurate when asked to judge the gender of walking human figures, even when they are represented by 15 small dots of light attached to major joints of the body.
And not only that, when human observers watched the walking motion of a male so-called "point light walker," they were more sensitive to the female attributes when watching the next figure in the sequence. This suggests that the human brain relies on specialized neurons that tell gender based on gait, report researchers at the Salk Institute for Biological Studies in the May 21 advance online edition of Nature Neuroscience.
"Our judgment of gender can adapt within seconds," says senior author Gene Stoner, a neuroscientist in the Vision Center Laboratory at the Salk Institute. "The gaits of males and females may vary geographically or culturally and this mechanism allows us to adapt very quickly to local ways of walking," he adds.
How humans move reflects, in part, gender-specific differences in shape such hip-to-waist ratio and the like. Such inherent differences in gait might then be exaggerated by an individual to emphasize their gender. "Our new data suggests that there are neurons selective for gender based on these motion cues and that they adjust their selectivity on the fly," Stoner explains.
Although much work has been done on how the brain represents so-called low-level features, such as "redness" or "left-moving," scientists have been unable to put their finger on more abstract concepts such as gender. "We wanted to know whether gender is represented in a similar way to low-level visual features such as color, or if it is a more semantic concept such as good and evil," says experimental psychologist and first author Heather Jordan, a former post-doc in the Vision Center Laboratory and now an assistant professor at York University in Toronto.
Individual neurons in the visual cortex are finely tuned to certain attributes of visible objects such as the color red, a certain shape or objects moving in a specific direction. These specialized neurons reveal their existence through a telltale effect called adaptation. For example, if you stare at a red patch and then look at a neutral color you tend to see green. This "adaptation" reflects a mechanism in the brain that exaggerates differences between objects to increase the sensitivity and optimize the output of individual neurons.
I think the ability to recognize differences is something that one could enhance with thoughtful control of one's environment. What differences do you want to get better at recognizing?
These scientists expect to eventually identify a single neuron that activates for male gaits and another neuron that activates for female gaits.
"In the past, when adaptation in behavior was observed for specific features, neurophysiologists have subsequently been able to find individual neurons which fire only when they encounter this feature," says Jordan. "We think that the same is true for maleness and femaleness - that there are neurons in the brain that fire if, and only if, they 'see' a male gait and others that fire if, and only if, they 'see' a female gait, explains Jordan.
"We know lots about individual neurons that are sensitive to the direction of moving objects. But in this case, motion provides information about the structure of what is moving," says Stoner.
The mind compares gaits to recently seen gaits of other walkers. So you are more likely to be seen as masculine after the mind has just seen an especially feminine walk and you are more likely to be seen as feminine after the mind has just seen an especially masculine walk.
For their experiments, the Salk researchers morphed the gait of averaged male and female walkers -- resulting in varying degrees of "maleness" and "femaleness" .When the figure consisted of less than 49 percent male contribution, the observers reported seeing a figure that appeared female. Once there was more than 49 percent maleness in the figure, they reported seeing a figure that was mostly male. But these numbers were not stable: Viewing the gait of one gender biased judgments of subsequent gaits toward the opposite gender. "If you want to appear particularly feminine you should walk behind a very masculine-looking male and vice-versa," jokes Jordan.
If it all comes down to individual neurons then I'd expect an age-related degeneration in the ability to recognize male versus female gaits. Should just the right neuron die then one might lose the ability to tell apart males and females. Though the odds of losing that neurons are low the odds rise with age. Though perhaps there's a mechanism where another neuron can take over the job if the one neuron doing the job dies or starts to misfire.
Given that there are individual neurons that consolidate information for a large assortment of pattern recognition tasks one might have a better chance of identifying loss of function due to deaths of individual neurons if one measured a large number of capabilities (e.g. ability to tell colors apart, direction of movement, various types of shapes, and ability to identify male and female gaits) through time. Error rates might rise before total failure sets in.
Question: If you've just heard a speech from an obviously dishonest person then are you likely to think the next person is honest if they sound relatively less dishonest? If so, this might explain why politicians and political activists can get away with telling so many lies. They get compared to each other rather than to an absolute standard of honesty.
More generally, are there specific types of images or other stimuli one could present to one's brain before examining some evidence or issue as a way to increase one's ability to see a contrast and recognize key differences?
|Share |||Randall Parker, 2006 May 28 08:07 AM Brain Sexuality|