The Inverted-face Effect
Source: Laboratory of Jonathan Flombaum—Johns Hopkins University
In perception, it is often the case that the ability to recognize and interpret compl…
1. Equipment and Stimuli
- This experiment requires a computer and experiment scripting software.
- In addition, the experiment requires a relatively large set of facial images, preferably with similar lighting conditions and without emotional expressions. Many databases of such images are available freely online for research purposes. A good resource is the MIT face database: http://web.mit.edu/emeyers/www/face_databases.html#oulu
2. Design
- Assemble a set of 80 facial images. Divide them in half, into two groups of 40. Use one group in the incidental exposure portion of the experiment, and reserve the other group to use as foils in the test portion.
- Note that your two groups should have the same relative proportions of males and females. In other words, if there are 25 male faces in one group of 40, there should be 25 in the other as well.
- The incidental exposure program
- The first part of the experiment involves incidentally exposing a participant to a set of 40 faces through a cover task.
- The experiment starts with a 'Ready' screen. Pressing the spacebar begins the exposure.
- Once the spacebar is pressed, each of the 40 faces is shown one-at-a-time for 1 s. After each image, a screen that says "Male/Female?" appears. (The cover task for the participant is to report whether a face was male or female.)
- Set the program to advance to the next face after the participant presses either the M or F key, (corresponding to Male and Female). Figure 1 schematizes the sequence of events in the exposure phase of the experiment.
- This phase of the experiment is a total of 40 trials-one for each face in the set.
Figure 1. Methods for an incidental encoding memory paradigm designed to demonstrate the inverted face effect. The experiment has two parts. In the first part, called the incidental-encoding phase, participants observe a set of 40 faces, one by one, and are asked to simply report whether each face is male or female. In the second phase, the participant is given a surprise memory test. In each trial, two faces are shown side-by-side. One of each pair is one of the faces shown in the encoding phase, and the other, called the foil, is a new face, never seen before by the observer. The task is to use the right and left arrow keys to indicate which face in each pair is the one seen previously. Crucially, half the face pairs appear upside-down. The measure of interest is report accuracy for right-side up compared with upside-down faces. Please click here to view a larger version of this figure.
- The test phase program
- The test part of the experiment also includes 40 trials.
- For each trial, randomly select one of the old faces and one of the previously reserved faces (of the same sex). Place one on the left side of the screen and one on the right.
- The task is for the participant to indicate with the left or right arrow key which of the faces in a pair was seen before.
- The crucial manipulation is that in half of the trials, the two faces are presented upside-down.
- Randomly intermix upside-down and right-side-up trials.
3. Running the Experiment
- Before the experiment begins, it is a good idea to ask the participant if she or he has any known visual impairments or difficulties, and in particular, if they think they have any difficulty recognizing people.
- Seat a participant 60 cm from the monitor of the presentation computer.
- Explain the encoding phase to the participant as follows, without mentioning the test phase to come:
- "This is an experiment about face perception. In each trial, you will see a single face for one second, followed by a screen in which you will be asked to identify the sex of the face you just saw. Press the M key for male and the F key for female. The task may seem very easy, as we are conducting a study with several experiments, some including easy-to-identify stimuli and some with digitally-altered, more challenging stimuli. The results, taken together, will help us understand the facial features used to recognize the sex of a face. Whether it feels easy or hard to you, please do your best. There are only 40 trials, and it will take less than five minutes to complete."
- Start the program and stand nearby as the participant completes this phase of the experiment.
- When the participant is done, say the following:
- “Thank you for completing that portion of the study. I would like you now to do a second experiment, one that will also last only five minutes. In each trial, you will see two faces, one on the left side of the screen and one the right side. One of the faces in each pair will be one of the faces you just saw, and the other will be a new face, one that did not appear in the judgment task you just did. Your task now is to identify the ‘old’ face, the one that appeared in the judgment task. Use the left arrow key to indicate the face on the left, and the right arrow key for the face on the right. In some of the trials, the two faces are shown upside-down. This is irrelevant—your task is always to do your best to identify the face that you think you saw once already.”
- Stand by as the participant completes the memory test.
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!
View the full transcript and gain access to JoVE Science Education videos
Q1: What is the inverted-face effect and why does it occur?
The inverted-face effect describes the difficulty people experience recognizing upside-down faces compared to upright ones, despite performing well with other inverted visual objects. This occurs because face recognition relies on specialized brain networks and computations tuned to process faces in their typical upright orientation. Poor performance with inverted faces suggests these dedicated facial processing mechanisms fail to engage effectively when orientation changes.
Q2: How is the incidental-encoding memory paradigm used to study face recognition?
The incidental-encoding paradigm presents participants with 40 faces for 1 second each, asking them to judge sex without mentioning a memory test. During the subsequent test phase, participants identify previously seen faces among foils, with half presented upright and half inverted. This design mimics natural face processing and measures memory accuracy across orientations, revealing the inverted-face effect through performance differences.
Q3: What brain region is specialized for processing upright faces?
The fusiform face area, or FFA, is a specialized brain region that shows stronger neural responses to upright faces than inverted ones. Neuroimaging studies using the inverted-face effect have identified this region as central to face recognition. Damage to the FFA can result in prosopagnosia, the inability to recognize faces including one's own, demonstrating its critical role in facial processing.
Q4: How do participants perform the incidental-exposure phase of the experiment?
Participants sit 60 centimeters from a computer and view 40 faces presented one at a time for 1 second each. After each face appears, they press 'M' for male or 'F' for female to indicate the face's sex. This 5-minute phase requires no memory encoding instructions, allowing researchers to study how faces are processed incidentally, without deliberate memorization effort.
Q5: What does poor performance on inverted faces reveal about face processing?
Poor performance on inverted faces, often near chance accuracy, indicates that specialized facial processing mechanisms are specifically tuned to upright orientations. Since faces are almost always encountered upright in natural experience, the brain's face-processing systems have evolved to exploit this statistical regularity. When faces are inverted, these specialized mechanisms fail to engage effectively, causing recognition to drop dramatically.
Q6: How is the test phase structured in the inverted-face effect experiment?
The test phase presents 40 trials with two faces displayed side-by-side: one previously seen and one new foil matched for sex. Participants press left or right arrow keys to indicate which face they recognize. Faces are randomly intermixed, with half upright and half inverted, allowing researchers to compare memory accuracy across orientations and quantify the inverted-face effect.
Q7: How can the inverted-face effect be used to diagnose prosopagnosia?
Prosopagnosia, or face blindness, results from damage to the fusiform face area and impairs face recognition regardless of orientation. Unlike typical individuals who show poor performance only with inverted faces, prosopagnostic individuals struggle equally with both upright and inverted faces. The inverted-face effect task helps diagnose this condition by revealing whether orientation-dependent deficits exist or if recognition is uniformly impaired.