Introduction

Face recognition is a mundane task that a socially active human may perform hundreds of times a day. Under normal circumstances, we find face recognition remarkably easy, but it is also possible to change the circumstances so that recognition becomes difficult. This will be illustrated in this demonstration experiment.

In trials of the experiment, you will see three face images at left: one on top and two side-by-side on the bottom. The top face will be a full-frontal view, while the images on the bottom will be profile views. Your task is to decide which of the two bottom images is of the same person depicted in the top image.

Instructions

Click the Start Trial button to begin each trial. You will then see three face images on the screen. When the images appear, click on the bottom image that you think is a picture of the same person in the top image.

Try to decide as quickly and as accurately as possible—you will be timed on how long it takes you to respond.

Results

Typically, people find this task trivial for normal, upright faces, but have much more difficulty (taking longer and making more errors) when the faces are inverted.

Furthermore, you may have found yourself looking at different aspects of the images for normal and inverted trials. With normal faces, the correct answer probably just “jumped out at you,” while for inverted faces, you may have had to resort to carefully inspecting individual features of the faces, such as eyebrows and lip color.

“Special” Face Recognition Processes

The inversion effect appears to reflect the fact that humans recognize upright faces differently than other objects. The type of processing used in identifying faces is often referred to as holistic, because when we see an upright face, we seem to analyze all the features of the face, as well as the relationships between features (How far apart are the eyes? How far is the nose from the mouth?), at the same time. With other objects (cars, houses, birds, etc.), we seem to process features in a more piecemeal fashion, and aren’t as attuned to details about the relations between the features. When a face is presented upside-down, our visual system treats it like just another object—the special holistic processing mechanisms that we usually bring to bear in face recognition apparently do not operate very efficiently on inverted faces. The fact that our “normal” object recognition processes have such difficulty with upside-down faces demonstrates that all faces are actually quite similar to each other. Normally, every face looks distinct to us because our holistic face recognition processes are so efficient at processing their fine details.

The inversion effect, as well as other sources of evidence, demonstrates that faces are treated as a special case by our object recognition system. But exactly why are faces special? This is currently a controversial research topic in the perception literature. Many researchers believe that a particular part of the brain (the fusiform gyrus in the right temporal lobe, if you want to know precisely) has evolved for the sole purpose of recognizing faces. This evolutionary adaptation would make sense, because face recognition is such an incredibly important part of humans’ social interactions. Other researchers contend that this part of the brain is adapted to process any type of object with which we have a great deal of experience recognizing (if you think about it, you’ve probably recognized faces far more often in your life than any other object). Supporting this position are experiments showing that expert bird watchers, but not non-bird watchers, show inversion effects for birds as well as faces; similarly, expert dog show judges show inversion effects for dogs.