cognition in clinical contexts

what is cognition

cognition is the processes by which the sensory input is transformed, reduced, elaborated, stored, recovered, and used. we cannot look inward to see cognition, so analogy and models are required.

4 aspects of cognition

1. experimental psychology - experiments with healthy human using large sample sizes and inferential statistics to determine success and significance.

2. computational modelling - computer simulations of cognitive processes, often involving parallel distributed processing. computer systems are made to reflect the inconsistencies that are present in the human brain.

3. cognitive neuropsychology - studying the consequences of brain damage or psychiatric disorders on cognitive function. case studies are important, and associations are used to reveal specifics of the mind.

4. cognitive neuroscience - studies how the brain implements cognitive functions using brain scans like EEG, fMRI and PET.

top down processing versus bottom up processing

Top-down processing uses prior knowledge, expectations and context to interpret information. Bottom-up processing builds an interpretation from incoming details, such as letters, sounds, shapes or data.

information processing models often assume a bottom up approach which means inputs are processed until an output is produced.

what is perception

perception refers to our ability to extract meaning from sensory input. it includes audition, taste, touch and olfaction but research is dominated by vision. vision alone accounts for over 50% of all neutrons in our cortex. but our senses are not limited to just 5 it is estimated to be from 9-27. most visual perception occurs in the visual cortex opposed to the eye. research supports that a near perfect representation of the external world is “projected” onto our primary visual cortex.

4 key sensory mechanisms

1. mechanoreception - detects physical distortion. responds to mechanical pressure, vibration, stretch, and movement. powers the senses of hearing, balance, and touch.

2. chemoreception - detects chemical substances. responds to specific molecules dissolved in air, water, or bodily fluids. powers the sense of smell and taste.

3. photorecepetion - detects light energy. responds to electromagnetic radiation within the visible spectrum. powers the sensory of vision using specialised rods and cones.

4. thermoreception - detects temperature changes. responds to heat and cold energy levels. powers the ability to monitor environmental and internal body temperature.

2 processing streams - ventral and dorsal

• the dorsal is the where pathway and is about sensory integration. information moves from the visual cortex to the posterior parietal cortex.

• the ventral is the what pathway. moves towards the inferior temporal cortex. the cerebral cortex receives the encoded images of the contralateral visual fields of both eyes.

object recognition model

we see an image

stage 1 is local features, this means we see the contrast and edge detection.

stage 2 is shape representation which is where gestalt principle occur and feature integration happens.

stage 3 is object representation where we store representation and knowledge. here we discover the specifics of an image.

object recognition is a constructive process not a passive one and it is rapid and effortless.

gestalt principles

• the core principles are similarity, proximity, closure, continuity, figure-ground (2D images are separated into a primary focal object and background to give a 3D effect) and simplicity.

• the whole visual percept is more than the sum of its parts

• our perceptual system constantly tries to impose organisation on its input

• components of an image are grouped together based on certain visual properties like colour, shape, or size

• laws of perceptual organisation e.g. good continuation where the eye follows the most continuous path rather than shifting abruptly and closure where our mind fill in missing gaps or spaces to perceive a complete shape.

• we make assumptions about situations based on our expectations.

shape perception

• primarily bottom-up processes produce a primal sketch

• this sketch contains primitives which includes edge, orientations, positions, lengths and colours

• top down processes are used to group collections of primitives together into lines, curves, larger blobs, groups and all patches

3 models of object recognition

template matching - the brain compares incoming visual data with copies or templates in long term memory. intuitively plausible - object recognition must involve some kind of contact with a comparable internal form.

feature analysis - Objects are deconstructed into a small, basic set of specific properties or components. assumes lower-level features are analysed first. the perceptual system searches for simple but characteristic features of an object.

recognition by components - we recognise 3D objects by breaking them down into basic volumetric geometric shapes called geons (short for geometric ions, such as cylinders, blocks, wedges, and cones). object recognition is impaired when neons are made non-recoverable by removing termination points.

Bruce and Young’s model of face recognition

• molecular model in that different sub-functions are processed independently and cannot be broken down further.

• distinct pathways for recognising familiar face versus recognising expressions like gender and facial speech recognition.

• facial recognition proceeds sequentially and one thing must happen before another thing.

• expression analysis, facial speech analysis and directed visual processing can happen in parallel.

• facial recognition units are linked to person identity nodes which are gateways to semantic information about the person. for example their job or where they are from.

• person identity nodes are linked to the final step which is name generation.

evidence for bruce and young

• most common errors are the person not being recognised, feelings of familiarity without identity, person recognised but no name retrieved and person misidentified.

• repetition priming found for familiarity decisions but not for gender or expression. if we see someone once we are more likely to be quicker identifying it again. however this does not work for gender decisions or facial expressions analysis.

neurological support for bruce and young

• parallelism - double dissociation between the processing of facial expression and face recognition. some have a deficit in identity but not expression and vice versa. some people can identify people but not what expression they are seeing and vice versa. this suggests that they are mostly separate.

• neuro-imaging - different cortical sites are active in the processing of identity versus emotion.

• in the inferior occipital and lateral fusiform gyro activity we can identify but not know expressions.

• in the amygdala and superior temporal sulcus activity it is the opposite.

challenge of semantic priming

• semantic priming is when a face is responded to faster if it follows a closely related face. e.g. prince Charles followed by Diana is recognised quicker than an unrelated face.

• a key limitation of bruce and young is that it cannot account for semantic priming. the model shows no obvious mechanism.

interactive activation and competition

• McClelland proposed parallel distribution networks that have interactive activation and competition build in as basic processes.

• concepts and category learning via and IAC model.

• semantic information is pooled. connections within a pool are mutually inhibitory. if one part of a pool is activated it prevents another aspect being activated.

• connections between pools are mutually facilitatory. different pools can all be activated at the same time.

• FRU activated inhibits others in the pool. this spreads out and connects to the PINs which goes to semantic information. this then goes back to PINs and moves to name input where a name can be produced.

• details of connectivity and spread of activation and inhibition clarified.

what do we use to recognise faces

• the challenge of reliably individuating faces is made apparent by the fact that all faces share a basic configuration.

• every individual face consists of facial features such as eyes, nose, and a mouth that have the same first order relations.

• although these features are ample for rendering the percept of a face, they are wholly inadequate in rendering a percept of that face.

• the efficacy of face coding for the purposes of recognition must exploit second order relations. e.g. the spatial interrelationship between features.

• stretching and shearing alter second order relationships, but faces remain easily identifiable. inverting is the hardest to recognise. negative faces are very difficult to recognise despite preserving the second order relationships (they are not sufficient for recognition)

• this means that second order relations are not necessary to the process.

• first order relations are the generic layout of the face whereas second order relations is specific distances and spacing between features.

where does face processing happen

• face processing is widely distributed and not completely localised but there are some core areas.

• core aspects are specific to the superior temporal sulcus and the inferior temporal cortex. this is where we see face selective neurons.

• for specific faces we can have neurons fire only for that face e.g. Jenifer Aniston.

hierarchical accounts of processing

• cells in the inferior temporal cortex are selective to complex stimuli giving credence to hierarchical theories of object perception.

• according to this view early visual cortex codes elementary features such as line orientation and colour. outputs are combined to form detectors of higher-order features such as corners or T-junctions. cells at the highest level in the hierarchy code specific shapes such as hands or faces.

Agnosia

• refers to impairment of visual object recognition unpeople who possess sufficiently preserved visual fields, acuity, and other elementary forms of visual ability to enable object recognition.

• typically occurs after damage to the occipital or inferior temporal cortex.

• does not mean there is loss of knowledge about objects.

• different types of agnosia reveal important clues concerning the processes underlying object recognition.

• damage is to the shape representation stage as they can identify local features but not identify the object.

1. apperceptive agnosia - able to move about and negotiate obstacles without difficulty. their grasp reveals knowledge of size and shape. low level binding of features appears to be absent. unable to perform basic copying and matching tasks.

2. associative agnosia - copying and matching skills are unimpaired. patient unable to name the object despite intact knowledge. involves a failure in accessing knowledge about the objects. for example if you asked what a key is they would know but if you point at a key and ask what it is they wouldn’t know.

prosopagnosia

• profound loss in ability to recognise faces usually due to right inferotemporal lesion.

• though unable to recognise previously familiar faces via visual input, recognition by other modalities remains intact. thus, individuals can be identified by their voices. the ability to recognise faces is tester through overt behavioural measures.

• covert recognition - prosopagnosic can recognised faces on an unconscious level. peak skin conductance responses occur 1-5 seconds after a face has been presented. peak amplitudes are larger for a familiar relative to an unfamiliar face. similar patterns are observed for prosopagnosic patients which suggests that there is a unconscious recognition without being able to name the person.

• similar to capgras delusion where a person can recognise a face and yet deny the identity of the individual. they often think family members are imposters. this is thought to be due to loss of activity in the dorsal stream whereas prosopagnosia is thought to be loss in the ventral stream.

case study for prosopagnosia

John is afflicted with visual agnosia and prosopagnosia – failure of object recognition and face recognition. He has completely forgotten how to read and now has no appreciation for gardens like he used to, he lost hard outlines. He can still identify something as a face, but he does not recognise his wife’s face. He recognises her by the sound of her voice and how she moves. Something moving helps him recognise better. Suffered a stroke which led to a lesion in his occipital lobes, in both hemispheres.  Cannot integrate features of objects. John makes visual errors as he misidentifies objects.