Cognitive Neuroscience chapter 6

The Hierachical Coding Hypothesis

Features (vertical edge, horizontal edge) ----> Conjunction of features (corners, length) ---> component shapes (rectangular surface, legs) ---> object/gnostic unit (table)

Alexia

Reading Impairment. A neurological syndrome in which the ability to read is disrupted. Alexia is frequently referred to as acquired alexia to indicate that it results from a neurological disturbance such as stroke, usually including the occipitoparietal region of the left hemisphere. In contrast, refers to problems in reading that are apparent during childhood development. The phrases and development dyslexia are commonly used to indicate that reading is abnormal, either from a neurological disturbance or as part of development. A type of associative agnosia.

Category Specific Deficits

Recognition impairment that is restricted to a certain class of objects. Some rare individuals demonstrate an impairment in their ability to recognize living things , yet exhibit near-normal performance in recognizing nonliving things. Such deficits are useful in the development of models about about how perceptual and semantic knowledge is organized in the brain. Explanations may be that semantic memory is damaged or that living objects are harder to recognize. Circumscribed lesions might destroy tissue devoted to processing similar types of information. Many believe manufactured objects are easier to recognize because they activate additional forms of representation, or action knowledge or the knowledge of how we interact with objects. (kinesthetic, motor).

How do patient studies support the what/where distinction?

Patient D.F. Had severe object recognition disorder. In task one she was given a circular block with a slot cut into it and asked to hold a card in such a way it could fit into the slot, she performed very poorly and could not recognize the orientation of the object. On task 2 she was asked to insert the card into the slot, and she oriented her hand just before inserting the card. This is further evidence of a distinction between where and what because the where pathway appears to be responsible for more than just spatial information, it is critical for guiding interactions with objects, calling it the HOW pathway would be better. While shape and orientation information were not available to the processing system for objects, they were available for the visuomotor task. Therefore where and what tasks may carry similar information but support different aspects of cognition.

Auditory Agnosia

Patients must perform within normal limits on tests of tone detection, or the loudness of a sound thats required for the person to detect it must fall within the normal range. Secondly, the deficit in recginizing objects must be restricted to a single modailty, such as a person who cannot identify environmental sounds such as a waterfall, must be able to recognize a picture of a waterfall. Amusia is an impairment in musical abilities.

Lateral Occipital Cortex

A region of extrastriate cortex that is a part of the ventral pathway. Processing in LOC is essential for shape perception and recognition.

Associative Agnosia

A failure of visual object recognition that cannot be attributed to a problem of integrating parts to form a whole, or to a perceptual limitation, such as a failure of object constancy. They can percieve objects with his visual system but cannot assign meaning to the objects. Reserved for patients who derive normal visual representations but cannot use this information to recognize things. Patients who are unable to access conceptual knowledge from visual input. Their perceptual abilities may be relatively intact, but they fail to link that representation to knowledge about what the object is used for, where it might be found, and so on. Patients who derive normal visual representations but cannot use this information to recognize things. These patients do well on coloring in different objects presented on a complex drawing as opposed to apperceptive agnosia patients, they just can't name those objects. A form of agnosia in which the patient had diffiuclty linking perceptual representations with longterm knowledge of the percepts. For example, the patient may be able to identify that two pictures are of the same object, yet fail yo demonstrate an understanding of what the object is used for or where it is likely to be found.

Integrative Agnosia

A form of agnosia associated with deficits in the recognition of objects due to the failure to group and integrate the component parts into a coherent whole. Patients with this deficit can faithfully reproduce drawings of objects; however. their precept is of isolated, unconnected parts or contours. An inability to integrate features into a coherent whole. This was exhibited by patient HJA who was able to name some objects on about 80% of trials, but fewer if they were shown to him in drawings, and when presented with overlapping figures, he failed completely. They have little trouble doing shape matching tasks and can match photographs of objects seen from unusual views unlike apperceptive agnosia. However when asked to identify objects that overlap one another, they experience extreme difficulty. This is because when they overlap the observer must not only identify the parts but also correctly assign the parts to objects. Ex. circle with two squares figure.

Parahippocampal Place Area (PPA)

A functionally defined area of the brain (usually with fMRI), located in the parahippocampal region of the temporal lobe that shows a preferential response to stimuli depicting scenes or places.

Grandmother Cells

A humorous term used to refer to the notion that there is a gnostic cell that is stimulated only by the face of one's grandmother. However is presents the problem that if the cell died we wouldn't be able to recognize our grandmother. Also it does not adequately account for how it is possible to perceive novel objects, and it does not account for how the gnostic unit for grandmother would have to adapt as grandmother changed over time.

Encoding Model

A model of how information in the environment is represented. Encoding models are used in fMRI to predict the BOLD response to different stimuli.

Optic Ataxia

A neurological syndrome in which the patient has great difficulty using visual information to guide her actions, even though she is unimpaired in her ability to recognize objects. Optic ataxia is associated with lesions of the parietal lobe. Patients can recognize objects but cannot use visual information to guide their actions. They tend to make awkward and inappropriate movements of their hands and eyes, have the opposite behavioral problems of patient D.F. and is associated with lesions of the parietal lobe. Can recognize objects, but cannot use the visual information to guide their actions. When they reach for an object, they cannot move directly toward it but rather grope about like a person trying to find a light switch in the dark. They fail to take obstacles into account as they reach for something and their eye movements present a similar loss of spatial knowledge.

View-Dependent Frame of Reference

A theory based on the idea that perception involves recognizing an object from a certain viewpoint. View-dependent theories assume that visual memory is based on previous experiences with objects in specific orientations and that the recognition of an object in a novel orientation involves an approximation process to the stored representations of specific perspectives. Perception is assumed to to depend on recognizing an object from a certain viewpoint. Specific representations are stored in memory, a stimulus is matched with a representation, and it has a heavy load on memory. People have a plethora of specific representations in memory and we simply need to match a stimulus to a stored representation. It places a heavy burden on perceptual memory in that we need to have multiple representation of objects from different angles stored in our memory.

View-Invariant Frame of Reference

A theory based on the idea that perception involves recognizing certain properties of an object that remain invariant, or constant across different perspectives. In this view, these properties form the basis of visual memory, and recognition entails matching the perceived properties of this knowledge base. Sensory input defines basic properties, developed by David Marr in 1982, says things have major and minor axes (major - wheels & handlebars, minor - seat & pedals). Also says that recognition depends upon inferences made based on a few salient features that hold across different vantage points. Recognition does not happen by simple analysis of stimulus information but rather the perceptual system extracts structural information about the components of an object and the relationship between these components. For example the properties might be an elongated shape running along the long axis combined with a shorter stick like shape coming off one end, and two circular shaped parts, then we would recognize the object as a bicycle from just about any viewpoint.

Ensemble Coding

An alternative hypothesis to the notion of Grandmother Cells that says rather than a single cell being responsible for object perception it is a group of cells. Some of the cells may respond to grandmother's shape, the color or her hair, or the features of her face. It accounts for why we recognize similarities between objects such as a lion and tiger, and may confuse on visually similar object with another.

Analytic Vs Holistic Processing in Visual Perception

Analytic processing is a perceptual analysis that emphasizes the component parts of an object. Reading is thought to be a prime example of analytic processing in that the recognition of words requires the analysis of at least some of the component letters. Analytical = word recognition. Holistic Processing is a perceptual analysis that emphasizes the overall shape of an object. Face perception has been hypothesized to be the best example of holistic processing, in that the recognition of an individual appears to reflect the composition of the person's facial features rather than being based on the recognition of the individual features themselves. Holistic = Face Recognition. The left hemisphere is more efficient at analytic processing (deficits result in alexia) and the right hemisphere is more efficient at holistic processing( deficits result in prosopagnosia). If a patient has prosopagnosia they will not also have alexia and vice versa.

Imagery (brain structures involved and deficits)

Brain areas that are active in visual perception are also active in mental imagery. (occipito-temporal pathway - inferior longitudinal fasciculus and the Occipito-parietal pathway - superior longitudinal fasciculus) Ex. seeing an apple activates the same areas as forming a mental image of an apple. Patients who have deficits in perception also have deficits in imagery. Visual perception and mental imagery are not the same thing, but they use the same brain areas.

Neural Areas Involved in Face Perception

Cells in two distinct areas of the temporal lobe are believed to be preferentially activated by faces: they superior temporal sulcus, and the inferior temporal gyrus. Also, the Fusiform Gyrus in the right temporal lobe is also active during facial recognition. Damage to the occipital lobe may also result in prosopagnosia.

Apperceptive Agnosia

Describes failures in object recognition linked to problems in perceptual processing. It can be very subtle and the primary deficit is in object constancy. The patient may perform normally on tests, but the object recognition problems become evident when the patient is asked to identify objects based on limited stimulus information, either because the object is shown in a line drawing or seen from an unusual perspective. Although these patients can recognize objects, this ability diminishes when the perceptual input is limited. This finding is most consistent in patients with right-hemisphere lesions, suggesting the right hemisphere plays a role in object constancy. A form of agnosia associated with deficits in the operation of higher-level perceptual analyses. A patient with apperceptive agnosia may recognize an object when seen from a typical viewpoint. However, if the orientation is unusual, or the object is occluded by shadows, recognition deteriorates.

Visual Agnosia

Disturbance of perceptual recognition that cannot be attributed to impairments in basic sensory processes, limited to the visual modality. Agnosia is derived from "gnostic" meaning to know. A failure of perception that is limited to the visual modality. In visual agnosia, the patient is relatively good at perceiving properties such as color, shape, or motion yet cannot recognize objects or identify their uses. They may only recognize an object when it is viewed from a certain angle, or be able to draw a picture of the object but not know what it is called or what it is for. Behaviors such as finger twitching indicate that they have access to knowledge of objects but access to that information is insufficient to allow him to come up with the name of the object.

Fusiform Body Area (FBA)

Same as EBA. A functionally-defined area in the lateral occipitotemporal cortex that has been found, in fMRI studies, to show a stronger response to images containing body parts relative to other animals and inanimate stimulus categories.

Extrastriate Body Area (EBA)

Same as FBA. A functionally-defined area in the lateral occipitotemporal cortex that has been found, in fMRI studies, to show a stronger response to images containing body parts relative to other animals and inanimate stimulus categories.

Occipito-temporal pathway

Specialized for object perception and recognition. "What" - Inferior Longitudinal Fasciculus follows a ventral route from the occipital striate cortex into the temporal lobe.

Occipito-parietal pathway

Specialized for spatial perception and locating objects in space. "Where" - Superior Longitudinal Fasciculus takes a dorsal path from the straits cortex and other visual areas, terminating mostly in the posterior regions of the parietal lobe.

Prosopagnosia

Term used to describe an impairment in face recognition. It is a disorder of object recognition, and like other visual agnosias it requires that the deficit be specific to the visual modality. They are able to recognize a person upon hearing their voice. They struggle to identify their families and even themselves. A deficit in the ability to recognize faces that cannot be attributed to a deterioration in intellectual function. A neurological syndrome characterized by a deficit in the ability to recognize faces. Some patients will show a selective deficit in face perception, a type of category-specific deficit. In others, the prosopagnosia is one part of a more general agnosia. Prosopagnosia is frequently associated with bilateral lesions in the ventral pathway, although it can also occur with unilateral lesions of the right hemisphere.

Object Constancy

The ability to recognize invariant properties of an object across a wide range of contexts. For example, although the size of the retinal image changes dramatically when a car recedes in the distance, our percept is that the car remains the same size. Similarly, we are able to recognize that an object is the same when seen from different perspectives. Our amazing ability to recognize an object in a variety of situations and from a variety of points of view. Visual information emanating from an object varies for several reasons, viewing position, how it is illuminated, and the object's surroundings. Object recognition must be general enough to support object constancy, and it must also be specific enough to pick out slight differences between members of a category or class.

Repetition Suppression Effect

The phenomenon seen during functional MRI in which BOLD response to a stimulus decreases with each subsequent stimulus repetition.

Gnostic Unit

The type of neuron that can recognize a complex object, or the idea that the cell signals the presence of a known stimulus, an object, a place, or an animal that has been encountered in the past. It is the top of the hierarchical structure of object perception.

What-Where Pathways

The what (ventral) pathway occurs in the central stream or the occipito-temporal pathway along the inferior longitudinal Fasciculus. It is specialized for object perception and recognition. The where (dorsal) pathway occurs in the occipito-parietal pathway along the superior longitudinal Fasciculus. It is specialized for spatial perception. Studies also suggest the separation of what and where pathways is not limited to the visual system, and may carry over into auditory processing regions.

Decoding

Using the brain activity, which is produced by a stimulus and detected by such methods as fMRI, in order to determine the original stimulus.