One of these two images contains a hidden picture of a face. Which one?
This was the question faced by participants in a remarkable psychology experiment just published, Measuring Internal Representations from Behavioral and Brain Data.
Five healthy volunteers were presented with a series of random black and white grid patterns. Each grid square was either black or white, and this was randomly determined on each trial.
There was no pattern to the images, they were completely random. But the subjects were told that half of the patterns contained a hidden face, and that their job was to work out which ones did. Each subject saw over 10,000 random images and they took about 1 second to judge each one.
The volunteers "detected" a face in 44% of the images. Somehow, all five of them convinced themselves that they were seeing faces in many of the grids. The authors say that
Upon completion of the experiment we debriefed observers, and all expressed shock that no face was ever presented.
That's strange enough in itself, but here's the really clever bit. The authors compared the patterns which were declared to contain a face, to the ones that were reported as empty. The image below shows the average "face" grid, minus the average "non face" grid, for each individual subject:
As you can see, this reveals...a face! Kind of. The top half shows the raw average; the bottom half shows the statistically significant differences from random noise.
In Subjects 1 and 2, the face is pretty clear, with eyes, a nose and a mouth. For 3 and 4, it's less coherent, but you might be able to see it if you look hard enough. For Subject 5, not really.
What this means is that people (at least, most of them) were not just seeing faces in any noise. They tended to see faces when the random patterns happened to resemble a kind of primitive face, but it was a different face for each person. The authors say that these strange faces correspond to the individual's internal representations, or models, of "a face", that each subject was "seeing" in the noise.
Finally, the whole experiment was conducted while EEG data was being recorded from the participant's brains. The EEG results revealed that there was a clear difference in the neural activity associated with "face" compared to "nonface" stimuli - except in Subject 5, who you'll remember had the least coherent "internal face".
What's exciting about this approach is that it investigates perception in a purely "top down" way. Normally, when we look at anything, what we end up perceiving is a product of "bottom up" influences - the raw data - and "top down" ones - what we expect to see. In this experiment, there was no real "bottom up" data; it was all "top down".
This is a form of pareidolia - perceiving familiar things in random stimuli. Seeing the face of Jesus in your sock, that kind of thing. It works for sounds too: in the famous White Christmas Experiment, people report "hearing" music in pure white noise - when told to expect it. Real-life examples of this include the "Islam Is The Light" doll, and my personal favorite, the singing paedophile Christmas mouse.
Finally, I wonder what embodied cognition theorists make of this paper. Because this paper claims to be "Measuring Internal Representations from Behavioral and Brain Data"; embodied cognition (at least the radical kind) is the theory that "internal representations" either don't exist, or at least don't explain anything about human cognition.
Smith, M., Gosselin, F., and Schyns, P. (2012). Measuring Internal Representations from Behavioral and Brain Data Current Biology DOI: 10.1016/j.cub.2011.11.061