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in facial recognition because damage to it makes it difficult or impossible to recognize the face of someone you know, even your own in a mirror! More specifically, there are two separate neural pathways: one for processing faces in general and another for processing facial characteristics in particular. This is done through two different types of neurons: large (magno) cells that comprise the relatively rapid-firing magnocellular pathway that processes large receptive fields and carries low-spatial-frequency (coarse-grained data) information (the general face), and smaller cells that comprise the relatively slower firing parvocellular pathway that processes small receptive fields and carries high-spatial-frequency (fine-grained data) information (facial details such as eyes, nose, and mouth).

Further, it appears that the brain first processes the global shape of a face, such as the general outline with two eyes and a mouth, and then processes the details of facial features, such as the eyes, nose, and mouth. This is why when you examine the upside-down photograph of President Obama (in figure 3) you recognize him immediately; but if you stare at it awhile you will see that there is something odd about his eyes and mouth in one of the pictures. Turn the book upside down and you will see what it is. This is the effect of your two different facial-recognition networks operating at different rates and granularity. First there is the rapid assessment that it is a face, and then the recognition that it is the face of someone you know; then there is the processing of the details of that face, which takes a bit longer. The former happens quickly and unconsciously while the latter happens slowly and consciously.11

This difference between slow and rapid processing of information is interesting because in the search for the neural correlates of consciousness, most theories hold that rapid unconscious processing happens before slower conscious awareness. In a famous 1985 study by neuroscientist Benjamin Libet, he took EEG readings of subjects sitting in front of a screen in which a dot was moving about a circle (like the second hand on a clock face). The subjects were asked to do two things: (1) note the position of the dot on the screen when they first became aware of the desire to act, and (2) press a button that also recorded the position of the dot on the screen. The difference between 1 and 2 was two hundred milliseconds. That is, two-tenths of a second lapsed between thinking about pressing the button and actually pressing the button. The EEG recordings for each trial revealed that the brain activity involved in the initiation of the action was primarily centered in the secondary motor cortex, and that part of the brain became active three hundred milliseconds before subjects reported their first awareness of a conscious decision to act.

Figure 3. Faces Everywhere

The human face is so important in the expression of emotions that we have evolved facial-recognition networks in our brains (see details in the text), to the point where we see faces everywhere we look. Here are a few examples.

a. The face on Mars, original grainy photograph from 1976 Viking spacecraft mission. COURTESY OF NASA.

b. The face on Mars, closer detailed photograph from 2000 Mars Surveyor mission. COURTESY OF NASA.

c. The happy face on Mars. COURTESY OF NASA.

d. Indian chief head or random configuration of hills and valleys? Configuration is in Cypress County, Alberta, Canada, southeast of Calgary just north of the U.S. border. Turn the book upside down to view the image from a different perspective or enter the coordinates (+50° 0' 38.20", −110° 6' 48.32") into Google Maps and zoom in on the image and rotate it yourself to see the face pattern appear and disappear. COURTESY OF GOOGLE MAPS.

e. Which upside-down photo of President Barack Obama looks odd? Turn the book upside down to find out (see the text for explanation). Original illusion was discovered by Peter Thompson of York University and published in 1980: PETER THOMPSON, “MARGARET THATCHER: