Chapter 7

Question 1

Cognitive neuroscience

Answer 1

Relating the properties of the underlying neuroscientific properties of the system to cognitive models of information processing.

Question 2

From eye to brain

Answer 2

Left space to right brain (not left eye to right brain).

Question 3

Quadrantanopia

Answer 3

Refers to an anopia (loss of vision) affecting a quarter of the visual field.

Question 4

Macular sparing

Answer 4

Many lesions at this level are due to stroke; sparing because occipital lobe receives blood flow from both posterior and middle cerebral artery.

Question 5

Geniculostriate pathway

Answer 5

Several pathways from eye to brain. Main route terminates in primary visual cortex (V1). Route is called geniculostriate pathway because it goes via lateral geniculate nucleus (LGN) and terminates in striate cortex (another name for V1).

Question 6

Lateral Geniculate Nucleus (LGN)

Answer 6

Contains six layers, three for each eye. Cells have a centre-surround receptive field. They respond to differences in light across their receptive field (e.g. presence of light in centre, absence in surround).

Question 7

Primary visual cortex (V1)

Answer 7

Extracts basic information from the visual scene (e.g. edges, orientations, wavelengths of light). This information is used by later stages of processing to extract information about shape, color, movement, etc. Single-cell recordings by Hubel and Wiesel lead to a hierarchical view of vision in which simple visual features (e.g. points of light, cf. LGN) are combined into more complex ones (e.g. adjacent points of lights may combine into a line).

Question 8

Cells of primary visual cortex (V1)

Answer 8

Simple cells may derive their response by combining the responses of several LGN centre-surround cells. Simple cells respond to different orientations. Complex cells may be derived by combining responses of several simple cells. Complex cells respond to orientation too, but are less sensitive to the exact position of the line in the receptive field (= invariance). Hypercomplex cells (outside V1) may be derived by combining the responses of several complex cells. Unlike complex cells, they are sensitive to length as well as orientation.

Question 9

Spatial arrangement of primary visual cortex (V1)

Answer 9

Retinotopy: the spatial arrangement of light on the retina is retained in the response properties of V1 neurons (except inverted). Damage to parts of area V1 results in blindness for the corresponding region of space (e.g. hemianopia).

Question 10

Cortical and sub-cortical damage

Answer 10

Damage to geniculo-striate route impairs conscious vision, but other aspects of vision spared (blindsight).

Question 11

Blindsight

Answer 11

Damage to V1 leads to a clinical diagnosis of blindness (the patient cannot consciously report objects presented in this region of space). However, the patient is able to make some visual discriminations in the blind area (e.g. orientation, movement direction) - called blindsight. This is because there are other routes from the eye to the brain. The geniculostriate route may be specialized for conscious vision but other routes act unconsciously. Filling in of blind regions similar to filling in of normal blind sport (most patients have hemianopia).

Question 12

Area V4 and area V5/MT

Answer 12

Area V4 is specialized for color: study colored images (Mondrians) compared to grayscale equivalents.
Area V5 is specialized for visual movement: moving dots compared to static dots.

Question 13

Color perception and area V4

Answer 13

Why does the brain need a specialized processing system for color given that the retina is already sensitive to different wavelengths of light? The problem is that wavelength depends on the composition of the light source (e.g. daylight, electric light) as well as the color of an object.

Area V4 tries to compute the color of the object taking into account variations in lighting conditions. This is called color constancy.

Cells in V4 continue to respond to the same surface color if the light source is changed, whereas cells in V1 do not.

Patients with damage to area V4 see the world in black and white – they have (central) achromatopsia (not to be confused with color blindness due to cone deficiency).

Although achromatopsic patients fail to see color, their retina and their V1 cells still respond to different wavelengths of light (e.g. they can see lines forming the boundary between two equiluminant patches with different colour).

This is another example of how visual perception is constructed, rather than the mere detection of physical properties in the environment.

Question 14

Movement perception and area V5/MT

Answer 14

Cells in V5/MT do not respond to color but 90% of them respond to particular directions of movement. Patients with bilateral damage to this region see the world in a series of still frames. They are said to have akinetopsia. The patients can detect movement in other senses (e.g. hearing, touch).

It is possible to discriminate biological from random motion, given an array of moving dots.

Brain imaging and neuropsychology suggest that this may use additional regions/mechanisms beyond the ones involved in determining the overall direction of movement (system!), including the posterior superior temporal sulcus.

Akinetopsic patients can discriminate biological motion.

Question 15

Visual illusions

Answer 15

Illusory objects and illusory motion activate same parts of brain as real vision.

Question 16

Beyond visual cortex

Answer 16

Visual cortex (striate and extrastriate) extracts basic visual information – colors, movement, shapes, edges. In order for this information to be used it needs to make contact with other types of information: (1) where the object is in space (and this can’t be computed from the retinal image alone), (2) what the object is.

Question 17

Stages of model of object recognition

Answer 17

(1) Early visual processing (color, motion, edges etc.), (2) grouping of visual elements (Gestalt principles, figure–ground segmentation), (3) matching grouped visual description onto a representation of the object stored in the brain (called structural descriptions), (4) attaching meaning to the object (retrieved from semantic memory).

Disorders can be mapped into this scheme.

Question 18

Visual agnosia

Answer 18

Characteristics:
(1) Problem in mid- and/or high-order visual processes necessary to recognize objects based on vision.
(2) Intact low-level visual processes.
(3) Intact knowledge about objects and thus intact recognition based upon other modalities.
(4) Intact alertness, intelligence, language.

Question 19

Distinction from Lissauer

Answer 19

(1) Apperceptive agnosia: disorder in forming a
coherent percept.
(2) Associative agnosia: disorder in recognition despite intact perception.

Useful clinically, but too simplistic given the many stages in the system.

Question 20

Combining parts into wholes: Gestalt Grouping

Answer 20

Constitutes the second stage of the model of object recognition. Integrative agnosia is a type of apperceptive agnosia in which grouping principles are disrupted. Patient HJA.

Question 21

Visual form (apperceptive) agnosia: patient DF

Answer 21

Bilateral damage to lateral occipital cortex. Symptoms: (1) no ability to copy or recognize line drawings of objects, (2) can recognize real objects based on color/texture, (3) intact knowledge of objects (e.g., drawing from memory), (4) can interact with objects (“vision for action”).

Question 22

Routes to object consistency

Answer 22

Object constancy achieved by mapping a potentially infinite number of visual depictions on to a finite set of stored descriptions of object structure. One suggestion is that the brain stores objects in a single viewpoint (the canonical viewpoint that contains the principal axis). In this account, object recognition involves view normalization from the seen viewpoint to the stored viewpoint (mental rotation). Another suggestion is that stored structural descriptions are accessed by matching feature-by-feature.
Modern terminology: invariance/tolerance.

Question 23

Object Constancy via View Normalization

Answer 23

Patients with right parietal lobe damage may be unable to recognize objects in unusual views, but able to recognize them in canonical views.
Other patients can recognize objects in all viewpoints (unusual and canonical) but cannot choose the correct orientation for an object.
The latter is called object orientation agnosia and it provides evidence that the principal axis is stored separately from other aspects of object recognition.

Question 24

Neural Substrates of Object Constancy

Answer 24

Monkey cells in IT (inferotemporal) cortex respond to very particular object attributes (e.g. corners, shapes) but are less concerned with where they are located in space (Gross, 1992). These are ideal conditions for computing object constancy. Results in a hierarchical model of object perception.

Question 25

Are Faces Special?: Prosopagnosia

Answer 25

Prosopagnosia = impairments of face processing that do not reflect difficulties in early visual analysis. (Also used specifically to refer to difficulty in recognizing previously familiar faces).

De Renzi (1986) – patient failed to recognize his own family but could do so by voice, clothes. Could match different views of faces and name other objects. Can be acquired or congenital.

Face recognition is a within-category discrimination (all faces look the same), whereas other object recognition is between category (e.g. distinguishing a pen from a cup). Maybe faces require different types of processing to other objects? Maybe faces are so important from a social/evolutionary perspective that they have a mechanism all to themselves? Or is it based upon experience?

Question 26

Different Aspects of Face Processing: Bruce and Young (1986)

Answer 26

Important proposals:
- Processing towards face recognition units = structural descriptions (view-invariant).
- Distinction between processing of familiar and unfamiliar faces (latter = direct route).
- Specific route for expression.
- Specific route for facial speech.

Question 27

Evidence for Bruce and Young (1986) Model

Answer 27

• Double dissociation between recognizing familiar faces and matching unfamiliar faces across different viewing conditions (face constancy).
• In face naming, it is often possible to retrieve semantic facts without retrieving the name but the reverse pattern is not found (i.e. name generation depends on semantic retrieval).
• Double dissociation between recognizing familiar faces and recognizing emotion, age and sex.
• Double dissociation between recognizing familiar faces and using lip-reading cues.

Question 28

Sensation

Answer 28

The effects of a stimulus on the sensory organs.

Question 29

Perception

Answer 29

The elaboration and interpretation of a sensory stimulus based on, for example, knowledge of how objects are structured.

Question 30

Retina

Answer 30

The internal surface of the eyes that consists of multiple layers. Some layers contain photoreceptors that convert light to neural signals and others consist of neurons themselves.

Question 31

Cone cells

Answer 31

A type of photoreceptor specialized for high levels of light intensity, such as those found during the day, and specialized for the detection of different wavelengths.

Question 32

Rod cells

Answer 32

A type of photoreceptor specialized for low levels of light intensity, such as those found at night.

Question 33

Receptive field

Answer 33

The region of space that elicits a response from a given neuron.

Question 34

Blind spot

Answer 34

The point at which the optic nerve leaves the eye. There are no rods and cones present there.

Question 35

Hemianopia

Answer 35

Cortical blindness restricted to one half of the visual field (associated with damage to the primary visual cortex in one hemisphere).

Question 36

Quadrantanopia

Answer 36

Cortical blindness restricted to a quarter of the visual field.

Question 37

Scotoma

Answer 37

A small region of cortical blindness.

Question 38

Retinotopic organization

Answer 38

The receptive fields of a set of neurons are organized in such a way as to reflect the spatial organization present in the retina.

Question 39

Ventral stream

Answer 39

In vision, a pathway extending from the occipital lobes to the temporal lobes involved in object recognition, memory and semantics.

Question 40

Dorsal stream

Answer 40

In vision, a pathway extending from the occipital lobes to the parietal lobes involved in visually guided action and attention.

Question 41

Figure ground segregation

Answer 41

The process of segmenting a visual display into objects versus background surfaces.

Question 42

Lateral occipital complex (LOC)

Answer 42

A region of the brain that is specialized for processing object shapes.

Question 43

Adaptation (or repetition suppression)

Answer 43

A reduced neural response to a stimulus or stimulus feature that is repeated.

Question 44

Category specificity

Answer 44

The notion that the brain represents different categories in different ways (and/or different regions).

Question 45

Face recognition units (FRUs)

Answer 45

Stored knowledge of the three-dimensional structure of familiar faces.

Question 46

Person identity nodes (PINs)

Answer 46

An abstract description of people that links together perceptual knowledge (e.g. faces) with semantic knowledge.

Question 47

Fusiform face area (FFA)

Answer 47

An area in the inferior temporal lobes that responds more to faces than other visual objects, and is implicated in processing facial identity.

Question 48

Prosopagnosia

Answer 48

Impairments of face processing that do not reflect difficulties in early visual analysis (also used to refer to an inability to recognize previously familiar faces).

Question 49

Categorical perception

Answer 49

The tendency to perceive ambiguous or hybrid stimuli as either one thing or the other (rather than as both simultaneously or as a blend.