How we so exactly recognize people

[Pengwuino]

Something really caught my attention yesterday. I was talking to someone at my university and i see someone walk by and i look for a brief second at their backside and i IMMEDIATELY knew it was one of my friends. How is the brain so capable of recognizing people? Out of the tens of thousands of people at this university, I can recognize people with almost perfect accuracy. This is confusing to me because I heard people and objects are simply recognized by approximate shape diagrams your brain creates when you first see them.

 

[hypnagogue]

The brain has special tools for the recognition of human faces above and beyond whatever resources are used to recognize miscellaneous visual objects. This is demonstrated e.g. by the existence of prosopagnosia, a disorder in which recognition of faces is impaired while (in some cases) recognition of other kinds of visual objects is left largely intact. An individual with prosopagnosia will be able to detect the individual visual features of a face but will not be able to have these percepts come together in such a way as to subserve normal facial perception and recognition; roughly, the parts don't come together to form a coherent perceptual whole. (see link for more)

Broadly speaking, the existence of specialized systems in the brain for facial recognition goes some way towards explaining how it is we're so good at recognizing people.

Of course, your anecdote involved seeing the body shape of another person, which doesn't involve face perception. I'm not aware of any differences between the way we perceive human bodies and the way we perceive objects in general. One guess I can hazard is that the person you recognized is more salient to you (emotionally/personally/cognitively) than most generic objects would be, which could in turn make it easier for you to recognize the person's figure.

 

[Homer Simpson]

and i look for a brief second at their backside and i IMMEDIATELY knew it was one of my friends.

Depending on whose backside it was, there might not be much mystery at all.

 

[Q_Goest]

H, interesting information about prosopagnosia. I looked around a bit but didn't find any information explaining in gory detail. What is different about the brain of someone with prosopagnosia and someone without? I see people with this type of condition can have it at birth and it may be genetic in origin, but others suddenly get this condition after a stroke or other brain damage. I'd be curious to know what is physically different or damaged in the brain and in the specific neurons. Any leads?

I wonder if recognition is a bit more general than just faces. For example, we might recognize specific buildings, our pets, our own car in a parking lot, etc just as rapidly as faces. There was some interesting research that just came out this past summer in the journal of Nature headed by Itzhak Fried.

The research, appearing in Nature, suggests that individual neurons are able to recognize people, landmarks and objects - even letter strings of names. The researchers say this indicates a consistent, sparse and explicit code that may play a role in transforming complex visual representations into long-term and more abstract memories. "This new understanding of individual neurons as 'thinking cells' is an important step toward cracking the brain's cognition code," said UCLA researcher Itzhak Fried.

"Our findings fly in the face of conventional thinking about how brain cells function," added co-researcher Christof C. Koch, from Caltech. "Conventional wisdom views individual brain cells as simple switches or relays. In fact, we are finding that neurons are able to function more like a sophisticated computer."

Ref: http://www.scienceagogo.com/news/20050523233706data_trunc_sys.shtml

Another fascinating article about single neurons recognizing specific objects is here: http://cbcl.mit.edu/cbcl/news/files/kreiman-hogan-5-05.htm

Many neuroscientists found it hard to believe that a single cell could recognize an inanimate object, let alone a human being. Even objects as simple as chairs, trees, or buildings come in an almost infinite variety of forms, and the same object looks different from different perspectives or in different contexts. Neuroscientists were therefore startled in the early 1970s when experiments on monkeys by Charles Gross of Princeton turned up cells that respond selectively to hands and faces--not specific faces but faces in general.

No one had really followed up on Gross’s findings, however, until the late 1990s, when Fried and his colleagues started reporting how epileptic patients reacted to various images. Some neurons were apparently smart enough to comprehend the highly abstract concept "non-human animal." Their neurons fired when the patient was shown a picture of a tiger, eagle, antelope, and rabbit, but not when shown pictures of humans or inanimate objects. Other cells favored images only of food, or of buildings, or of human faces. Some cells responded to all faces, but others were picky, firing for male faces but not female ones, or scowling faces but not smiling ones—or, finally, faces of specific individuals.

One of the first neurons of this type was the so-called Bill Clinton cell, which was buried deep in the amygdala of a female patient. The cell responded to three very different images of the former President: a line drawing of Clinton laughing; a formal painting of him; and a photograph of him mingling with other dignitaries. The cell remained mute when the patient viewed images of other people, including male politicians and celebrities. Fried’s group found cells in other volunteers that responded in this same highly selective way to actors, including Jennifer Anniston, Brad Pitt, and Halle Berry.

One reason celebrities have played a prominent role in Fried’s experiments is that their photographs are often easier to come by than images of a patient’s own relatives. But as part of her dissertation project on biographical memory, the UCLA graduate student Viskontas has for several years been showing patients photographs of family members. Viskontas is reluctant to reveal details about her results, which have not been published yet. But she confirms that she has found neurons that respond to a particular relative: father, mother, brother, sister, grandfather, and, yes, grandmother. The experiments have also found cells that light up when a patient sees an image of himself. Call them narcissism cells.

 

[hypnagogue]

H, interesting information about prosopagnosia. I looked around a bit but didn't find any information explaining in gory detail. What is different about the brain of someone with prosopagnosia and someone without? I see people with this type of condition can have it at birth and it may be genetic in origin, but others suddenly get this condition after a stroke or other brain damage. I'd be curious to know what is physically different or damaged in the brain and in the specific neurons. Any leads?

I don't think there is a wide consensus yet on what the answer to this question is. Some occipitotemporal areas of the brain (regions near the boundaries separating the occipital and temporal lobes) are known to be consistently more active during face perception, particularly the fusiform gyrus. But there is debate over whether or not activity in the fusiform gyrus itself is sufficient for face recognition-- if it's not, then some other areas must be involved as well.

e.g. some evidence for fusiform gyrus as face recognition area:
http://64.233.187.104/search?q=cache:2CsxGr5xXUcJ:www.arts.uwaterloo.ca/~jdancker/fMRI/oriet%2520FFA.ppt+fusiform+gyrus&hl=en

and some evidence against:
http://journalofvision.org/2/7/562/

I wonder if recognition is a bit more general than just faces. For example, we might recognize specific buildings, our pets, our own car in a parking lot, etc just as rapidly as faces.

Although the specific brain correlates may not yet be known, it is unambiguous that face recognition does not entirely result from some general object recognition systems in the brain. (If that were the case, for instance, prosopagnosia should not exist.)

The question of how rapidly we recognize miscellaneous objects as compared to faces is surely an empirical one. If there were any difference, it would be on the order of milliseconds, certainly not enough for us to discern by introspection. I'm sure some studies along those lines (measuring response times to face recognition compared to non-face recognition) have been conducted if you're interested in digging deeper.

In any case, I'm not sure response time would be the measure of most interest. Given that we do have specialized systems for face recognition, what do they do that is so specialized? I doubt their job is to help us recognize faces faster than other objects, although that effect might exist nonetheless. I'd guess that their job is to make us more sensitive to differences in the visual content of faces than we would be otherwise. There's a clear evolutionary advantage that could be had from devoting special resources to face recognition such that individuals are very good at discerning one face from another (better than they would be just by relying on general object recognition capabilities) and tying memories and attitudes and so on to those faces, etc.

It's interesting that there are neurons that respond selectively to most kinds of objects (like buildings, non-human animals, etc.), but this doesn't necessarily imply that we have specialized systems for recognizing these object categories as we do for faces. If that were so, for instance, I would expect that there would be a kind of disability where one's visual system is fully intact, except for a curious inability to recognize buildings. I'm not aware of such a phenomenon existing.