We don’t try to detect and recognize faces—it just happens, incidentally.
Impressively, for successful recognition, complex and demanding computations must occur in dedicated brain networks to integrate separate features into a cohesive face.
While recognizing faces right side up is relatively easy, identifying them in an upside-down position is far more difficult, even though this is not true for other kinds of visual objects.
This is often referred to as the inverted-face effect, and is used in experiments designed to investigate how face recognition takes place both cognitively and in the brain.
This video will demonstrate how to design and execute, as well as how to analyze and interpret an experiment investigating the inverted-face effect via an incidental-encoding memory paradigm.
In this experiment, participants are asked to judge male and female faces in two difference phases: incidental exposure and testing.
During the first incidental-exposure part, the participant is shown a set of 40 faces, one-at-a-time for 1 s each.
After every image is displayed, the participant is asked to report whether it was male or female by making an associated key press. This process mimics our natural ability to process faces—incidentally, without knowing it.
Then, for the second, test phase, the participant is shown two faces side-by-side. One is randomly chosen from the incidental-exposure portion and the other, called the foil, is sex-matched and never seen before by the participant.
Faces in the testing period are also randomly intermixed, with half of them upside-down and the other half, right side up. The participant is asked to indicate which of the two was seen previously.
In this case, the dependent variable is the number of faces correctly identified—a simple measure of memory accuracy—across upright and inverted orientations.
Participants are expected to perform better at recalling previously seen faces when they are shown upright, as opposed to inverted. Poor performance when identifying the inverted faces is known as the inverted-face effect.
Before starting the experiment, verify that the participant does not have any known visual impairments or difficulty in recognizing people.
To begin, seat the participant 60 cm from the presentation computer. Explain the instructions for the incidental-exposure phase without mentioning the test phase to come.
Start the program and stand nearby as the participant performs the first phase of the experiment and completes 40 trials in a 5-min period. Note that they see a single face for 1 s, and identify the sex of the face by pressing the 'M' key for male or 'F' for female.
Following the initial phase, thank the participant for completing this portion of the study and inform them of the instructions for the next test phase.
Once again, start the program and stand nearby as they complete the second memory phase of 40 trials. In this part, note that the participant presses either the left or right arrow key to indicate which face was observed previously.
To analyze the data, simply calculate the proportion of faces correctly identified and graph the results of memory accuracy by trial type: upright versus inverted.
Notice that for most visually normal participants, the accuracy is much higher when identifying faces that are upright as opposed to inverted, demonstrating the inverted-face effect.
Poor performance with the inverted ones—near chance—suggests that specialized facial processing mechanisms are tuned to take advantage of the fact that they are almost always experienced in an upright orientation.
Now that you are familiar with the complexity involved in processing inverted faces, let’s examine additional research scenarios where the effect can be applied.
Neuroimaging studies have used the inverted face effect to identify brain regions involved in specialized face processing.
Upright faces produce a stronger neural response in the fusiform face area, or FFA, than inverted ones, suggesting that inverted faces fail to engage specialized face-processing neurons.
In addition, brain damage to the FFA may result in a disorder known as prosopagnosia—the inability to recognize faces, including your own.
The task is often used to diagnose face blindness, as prosopagnostic individuals typically have just as much difficulty identifying right-side-up faces, as they do with those that are inverted.
You’ve just watched JoVE’s introduction to the inverted face effect. Now you should have a good understanding of how to design and conduct this type of experiment by implementing the encoding of a series of faces and retrieving familiar faces by memory. You should also know how to analyze and interpret the results.
Thanks for watching!