Face Perception

Superior temporal gyrus

auditory speech

Prosopagnosia: Etiology

A person can get prosopagnosia two different ways: It can be acquired or it can be developmental/congenital (condition present at birth)

Acquired Prosopagnosia

Acquired prosopagnosia is due to brain injury. Most often the brain injury is in the right occipitotemporal region.

Apperceptive Prosopagnosia

Apperceptive prosopagnosia is an inability to make sense of faces. Ex. the man who mistook his wife for a hat.

Associative Prosopagnosia

Associative Prosopagnosia is an inability to recognize individual faces. Associative prosopagnosics can often still perform face-matching. This is similar to the picture copying ability of associative object agnosia. People can process the eyes, nose, mouth, but they can't process the space between. It is an absence of knowledge.

Capgras Delusion

Belief that significant others have been replaced by imposters, robots, or aliens.

Developmental/ Congenital Prosopagnosia

Developmental/Congenital prosopagnosia is a lifelong difficulty with no obvious cause, there is a genetic component to it. This was originally thought to be very rare, but is now considered much more common that the acquired variety. People often just don't realize that they have this difficulty.

Faces are special: Developmental

Early Face preference

Faces are special: Neural Selectivity

Face selective regions

Human Neuroimaging

Haxby, Sergent and Puce studied this. Kanwisher came up with a cute name called the fusiform face area. This is the part of the brain that is believed to be specialized for facial recognition.

Inversion Effect

Inverting faces and objects impairs subsequent recognition, people have a harder time recognizing inverted faces and objects. This effect is disproportionately larger for faces than for objects. Impaired recognition is due to inverted faces being processed less holistically than upright faces. A famous example of this is the Thatcher Illusion. The face upside down might look normal, but when you turn it right-side up it looks horrifying. This is because we don't normally see faces upside down so we are processing it more like an object, looking at the normal individual parts instead of looking at it more holistically.

OFA and face detection

OFA serves as a face detector. It handles early perception of facial features. The OFA processes face parts regardless of configuration. The OFA responds to physical changes between faces. The area of greatest brain damage overlap in prosopagnosia patients is in the OFA not the FFA, we don't know why;.

Intracranial EEG

Places electrodes directly on the exposed surface of the brain to record electrical activity from the cerebral cortex. It is a way to study differences in face processing. You can see some sites that are face-specific.

Faces are special: Clinical

Prosopagnoisa (face blindness)

Prosopagnosia

Prosopagnosia is clinical evidence for faces being special. It is an impairment in the visual recognition of faces. There are two types of prosopagnosia: apperceptive prosopagnosia and associative prosopagnosia.

Prosopagnosia: Beyond Face Identity

Prosopagnosia sometimes goes beyond just a visual impairment in recognizing faces. In some cases it includes inability to recognize gender, emotion, and gaze direction. In other cases, other aspects of face processing are preserved. There are a few reports of patients with compromised emotion and gaze recognition, but normal identity recognition.

Capgras Delusion vs. Prosopagnosia

Prosopagnosias can have covert knowledge of a face, this means that somewhere in their brain they are processing it, they just don't have a conscious understanding of it. They have an affective (causing emotion) tag without any recognition. Capgras patients show the opposite. Capgras patients have recognition with an affective tag. Capgras is also only acquired.

Holistic Processing: Composite Face Effect

The composite-face effect shows up when two faces are split horizontally and stuck together. It's easier to identify the top half-face when it's misaligned with the bottom one than when the two halves are fitted smoothly together.

Face sensitive brain regions

The core system for perceptual processing of faces includes the OFA (inferior occipital gyrus), the pSTS (superior temporal sulcus), and the FFA (lateral fusiform gyrus)

The Expertise Theory

The expertise theory argues that the brain does not have areas dedicated to facial processing. The brain only has areas dedicated to subordinate level processing, aka it isn't about faces, its about expertise. We have been looking at faces since we were born. These regions are recruited when we need to distinguish between similar objects for which we have experience and expertise.

OFA

The ofa stands for inferior occipital gyrus. This part of the brain is for early perception of facial features.

pSTS

The pSTS stands for superior temporal sulcus. The superior temporal sulcus is for processing face movement and changeable aspects of faces such as eye gaze or expression.

Secondary systems for facial processing

There are also some systems that are important, but not dedicated to facial processing. These are the intraparietal sulcus, precuneus, superior temporal gyrus, amygdala (anterior insula), anterior temporal, rostral paracingulate

Support for Prosopagnosia being face-specific part 2

There are cases of object agnosia with spared face recognition. Patient C.K had integrative object agnosia. He had a difficult time seeing things on top of each other or all together. However, he could see faces. Faces have the same amount of objects, but C.K had no trouble when it is a face.

Support for Prosopagnosia being face-specific (against the expertise theory)

There are cases of prosopagnosia with spared object recognition even for expert categories. Patient W.J was a sheep farmer. He could not recognize human faces, but he had no problem identifying his sheep by their faces. Patient R.M could provide details for his miniature cars, but he could not recognize human faces.

Are Faces Special: Developmental: Early Face Processing

There is evidence for early face recognition specific to faces. Newborns as early as 9 minutes old prefer to look at faces than other types of visual stimuli. Also, newborns prefer faces with eyes open and those with direct gaze. There seems to be a critical period for face perception. Babies with congenital cataracts ultimately have compromised face discrimination. Also, 2-3 week old infants will mimic facial expressions.

Faces are special: Cognitive

There is the inversion effect and holistic processing

Support for the expertise theory

There was a farmer who acquired prosopagnosia and he lost the ability to individuate his cows. He was an expert in cows and lost this ability at the same time when he acquired prosopagnosia. Also, patients with prosopagnosia often suffer other defects such as: object agnosia, achromatopsia (color blindness) and topographic agnosia.

Are faces special: Neural selectivity: Face Selective Regions

They tested in monkeys and found that we have specific cells in our brain that fire to faces. They fire less when you remove eyes from the face. They don't fire to hands.

Are Faces Special: Cognitive Evidence

This comes down to what tests can we do to see if faces are processed differently.

Category-Specific Agnosia

This is a recognition deficit for some object categories but not for others. Some people experience it with living vs. non-living, fruits and vegetables, topographic agnosia (place blindness), or prosopagnosia (face blindness)

pSTS and expression/gaze

This processes eye and mouth motion, gaze direction, and facial expression.

Faces as social displays: gaze

We have a high contrast sclera in order to advertise gaze-direction. We have the whites of our eyes because we are so interdependent and social that it makes it clear what we are looking at. With other animals, the pupil is not in stark contrast, hiding attentional focus. Alsom newborns prefer looking at faces with open eyes and direct gaze. We reflexively orient our attention to the target of another's gaze, this is seen as early as 10 weeks old. Gaze is the best predictor of autism, autistic children don't follow gaze.

Faces as social displays: expression

We have evolved to have a hairless face so that we can see fine muscle movements in the face. It has been proven that we smile more broadly in social situations than we do when alone. Frequency and intensity of facial expressions increases during social situations. Expressions of primary emotions are universal. For example, in every culture people smile when they are happy. This suggests that these expressions are innate. It is further supported by the ability of newborns to imitate expressions.

Holistic Processing: Face Superiority Effect

We recognize objects by parts, but faces as a whole. For houses, it doesn't matter whether the door is in isolation or part of the house, we still know it is the same door. However, with a nose we might not be able to as easily same it is the same nose in isolation as the one on the person's face. This is because we memorize the whole face, holistic processing. If the nose is put back on the face, we can tell whether it is the same nose as before or not more easily.

Cortical Stimulation in Humans

When you stimulate certain areas, you can disrupt the brain's normal processing.

Capgras is a mirror of prosopagnosia

With prosopagnosia: there is visual input to the striate cortex and covert knowledge is sent to the limbic system. With capgras: there is visual input to the striate cortex and only overt information is sent to the limbic system.

Are faces special?

Yes. They are special in clinical ways, cognitive ways, development ways, and neural selectivity ways.

Anterior temporal

biographical knowledge

Amygdala, anterior insula

emotion

Superior temporal sulcus

intentions of others

Precuneus

retrieval of LTM images

Pareidolia

seeing faces in objects that aren't faces.

Intraparietal Sulcus

spatial attention

FFA

the FFA stands for lateral fusiform gyrus. The lateral fusiform gyrus processes invariant aspects of faces for perception of unique identity

FFA and identity

the FFA, lateral fusiform gyrus, is particularly sensitive to changes in perceived identity, rather than physical changes. The FFA only responds when the faces transition across identities. People don't process a continuous face shift, instead we start to notice when it is 70% one person.

Rostral Paracingulate

theory of mind, personal attributes