I. Face Perception

II. Visual Imagery

Is Face Recognition Special?

• Arguments have been made for both functional and neuroanatomical specialization for face processing (different from objects)

• Sources of evidence:– Behavioral experiments– Brain injury– Brain imaging

Farah (1994) experiment

Adapted from Farah, M.J., Specialization Within Visual object Recognition: Clues from Prosopagnosia and Alexia, in Farah, M.J., and Ratcliff, G. (Eds.), The Neuropsychology of High-Level Vision: Collected Tutorial Essays. Hillsdale, NJ: Lawrence Erlbaum Associates, 1994, pp. 133–146.

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Adapted from Farah, M.J., Specialization Within Visual object Recognition: Clues from Prosopagnosia and Alexia, in Farah, M.J., and Ratcliff, G. (Eds.), The Neuropsychology of High-Level Vision: Collected Tutorial Essays. Hillsdale, NJ: Lawrence Erlbaum Associates, 1994, pp. 133–146.

Results

Adapted from Farah, M.J., Specialization Within Visual object Recognition: Clues from Prosopagnosia and Alexia, in Farah, M.J., and Ratcliff, G. (Eds.), The Neuropsychology of High-Level Vision: Collected Tutorial Essays. Hillsdale, NJ: Lawrence Erlbaum Associates, 1994, pp. 133–146.

• Farah (1994) experiment suggests faces are perceived holistically. Suggests that the perception of the face is determined by all parts of the face.

• A demo of holistic processing:

Do these faces have anything in common?

How about these ones? By disrupting holistic processing, it becomes easier to process the individual parts

Effects of Inversion

• Humans are attuned to upright faces. Face perception is severely disrupted by inverted faces. This effect is less with objects

Thatcher illusion

What do Al and Bill have in common in this picture?

Is Face Recognition Special?

• Some evidence from behavioral experiments:

– Faces are processed holistically (Farah, 1994): difficult to separately process the parts of faces

– Inverted faces are more difficult to recognize or process than inverted objects

Neuropsychological evidence

• Face specific deficits found in prosopagnosia

• Subjects can identify most objects, but are impaired at recognizing faces

• Can name faces from touch and verbal descriptions so prosopagnosia is not a naming deficit visual pattern recognition problem

• Is it specific to faces or any difficult recognition problem?

Prosopagnosics can perform well on difficult object discrimination tasks

Brain Imaging Evidence

• In humans, face perception is uniquely associated with activity in the fusiform face area located in the fusiform gyrus in the inferior temporal lobe

• This finding is more robust in the right vs. left hemisphere.

What else can this area learn?

• We are well practiced for faces• How about training novel objects: Greeble learning

experiment. Over 10 hours on naming Greeble objects

Result

• After learning, the “face area” has become the Greeble area

What about real-world experts?

• Fusiform area is active for objects that you are an expert in

Evaluation

• Maybe faces are not processed so differently from objects. Depends on your level of expertise with objects.

• Holistic processing also occurs with familiar objects

• Fusiform gyrus can be activated by objects with which we have expertise

Visual Imagery

Visual Imagery

• Kosslyn and Thompson (2003, p. 723)– “Visual mental imagery occurs when a visual

short-term memory (STM) representation is present but the stimulus is not actually being viewed; visual imagery is accompanied by the experience of ‘seeing with the mind’s eye’.”

Study of Imagery

• Banned by behaviorists

• Possible subject of study in cognitive psychology– Cognitive psychology is distinguished from the earlier

behaviorism by its claim that there are internal representations of knowledge on which the mind operates

– However, this is a difficult area of study• Mental images are subjective• How can we show that images are used?

Some Questions about Mental Images

• How are mental images represented? Are they processed as visual images?

• What is the relationship between imagery and perception?

• How are mental images processed and transformed?

Study of Perception

Visual Input

Low Level Vision

High Level Vision

Knowledge

“LOOK AT THIS IMAGE”

Study of Imagery

Visual Input

Low Level Vision

High Level Vision

Knowledge

“IMAGINE A CAT UNDER A TABLE”

Mental Rotation

• Can mental images be transformed and how could we tell?

• Mental rotation task: look at the time it takes to rotate two shapes into correspondence

• Demo experiment:http://www.uwm.edu/~johnchay/mrp.htm

Example Trials

same different

different different

same different

different different

Results

• linear relationship between rotation and reaction time in object comparison

• The mental process seems to be analogous to the physical process of rotation.

Similar Results with Letter RotationThe different degrees of rotations performed on the materials in for mirror-imaged letters and normal letters

Cooper and Shepard (1973)The mean time to decide whether a visual stimulus was in the normal or mirror-image version as a function of orientation

Imagery & Perception

• Perceptual Anticipation theory (Kosslyn): mechanisms used to generate mental images also involve processes used to perceive stimuli.

• Prediction– Mental images should be quasy pictorial– Mental images should activate some of the brain

areas involved with visual processing

Just as in visual images, level of detail in mental images can vary

Does a rabbit have eyebrows?

Imagine a bee next to a rabbit Imagine a elephant standing next to a rabbit

Does a rabbit have eyebrows?

Finke and Kosslyn (1980) experiment

fixation dot separation

Angle of separation

Experiment measures field of resolution: the angle of separation into the visual periphery where you cannot distinguish dots any longer

Fields of resolution are similar in perception and imagery

Horizontal and vertical fields of resolution in perception and imagery as a function of dot separation and vividness of imagery. Data from Finke and Kosslyn (1980).

Evidence from Brain imaging (fMRI) for involvement of visual processing areas during visual imagery

(Le Bihan et al., 1993)

Imagery and Ambiguous Figures

How are mental images of ambiguous figures processed?

If you see one interpretation, it is very difficult to then imagine the other interpretation (unless you are trained in this task)

One difference between imagery and visual perception: visual images, unlike mental images can be easily reinterpreted

Mental Images might miss important aspects of object being imagined

• Imagine you have a cube between your thumb and index finger. One corner of the cube touches your thumb, and the diagonally opposite corner touches your index finger. Now, point to the locations of the rest of the corners in space.

Many people point (incorrectly) to four points on the same plane half way between the top and bottom corners.

Correct Solution:

Analog vs. Propositions Debate

• The analog vs. propositional debate– analog: the representation has the same structure as

the thing represented (e.g., Kosslyn)– propositional: a sentence-like description of the

image, non-spatial (e.g., Pylyshyn)

• Most studies mentioned seem to argue for analog representations (e.g., mental rotation, brain imaging studies). Supports Kosslyn’s perceptual anticipation theory

• Yet mental images are not processed exactly the same as visual images (ambiguous figures & cube demo)