IBP: Introduction to cognitive psychology

Chapter 4: Disorders in perception and attention

Synaesthesia: A condition in which individuals presented with sensory input of one modality consistently and automatically experience a sensory event in a different modality

• For example: seeing colour on hearing musical notes
• Illustration of how a synaesthete would see numbers compared to how non-synaesthetes see them: http://www.scielo.br/img/revistas/dn/v9n1//1980-5764-dn-09-01-00016-gf02.jpg
• Inducers: The triggers of synaesthetic experience
• Synaesthesia is usually a unidirectional process; the letter A may give rise to the perception of red but not vice versa.
• Synaesthetes are usually highly consistent – e.g.: Monday is always the smell of cheese
• Even when blind, synaesthetes see colours on hearing or thinking about letters or numbers
• Brain-imaging studies of synaesthesia:
  • Functional magnetic resonance imaging (fMRI)
  • Electroencephalography (EEG)
  • Transcranial magnetic stimulation (TMS)
• Most neural accounts of synaesthesia are based on the idea that regions related to the perception of the inducer (e.g. letter reading) become linked to regions related to the experience (e.g. colour perception) such that the occurrence of the former automatically activates the latter
• Certain hallucinogenic drugs such as LSD can induce temporary synaesthetic experiences in non-synaesthetes, suggesting that the pathways connecting the different sensory modules exist in normal brains

Blinsight: the ability to respond to visual stimuli without consciously perceiving them

• Scotomata (plural of scotoma): The areas of blindness
• Perhaps blindsight patients are responding to light which was reflected from the object onto the functioning areas of the visual field
  • This doesn’t explain, however, how the patients can distinguish between X’s and O’s
• While patients do not have any conscious experience of perception, at some level below that accessible to introspection, the visual system does have access to information about the outside world.
• The most widely accepted explanation for blindsight is that we have two separate visual systems, one primitive non-striate system and a more advanced striate system
  • The primitive non-striate system: might be sensitive to movement, speed, and other potentially important characteristics of a stimulus without giving rise to conscious perception
  • Striate visual system: conscious perception. Perhaps it has evolved to allow the identification of an object, whereas the non-striate system has evolved to allow the localisation of that object in space

Unilateral special neglect: A difficulty in noticing or acting on information from one side of space typically caused by a brain lesion to the opposite hemisphere (e.g. right-hemisphere damage producing lack of awareness for information on the left)

• The main cause of unilateral spatial neglect (USN) is stroke, an interruption to the brain’s blood supply
• Patients with USN may fail to notice object in ‘clear view’ on the left, ignore people approaching from the left, eat food only from the right side of the plate, or wash and dress only the right side of their own body.
• The most obvious difference between USN and visual field loss is that the former can exert an influence across modalities whilst the later is restricted to vision.
• USN varies in different spatial frameworks, it may occur for objects to the left side of the body (egocentric space) or for objects on the left side of something (like a page or room) regardless of where this is in relation to the person (allocentric space)
• A common clinical observation is that patients with persistent (chronic) left neglect tend to be drowsy and appear to have difficulty remaining focused on all sorts of tasks.
• Alerting patients with a loud tone temporarily but dramatically reduced or reversed their neglect, even when the tone was to their right. Stimulating medication or thoughts can cause similar gains.
• An important factor influencing whether a given stimulus will win the competition for conscious awareness is therefore the state of activity relevant to that stimulus across all levels of the system
  • Within this framework it is easier to see how unilateral brain damage could have cascading effects reducing the likely awareness of different sorts of information in contralesional space

Visual agnosia: the failure to recognise objects that are seen

• Apperceptive agnosia: patients have normal visual acuity with an inability to draw an object, to say whether two similar objects were the same or different, or even to describe the component parts of an object
• Associative agnosia: someone suffering from associative agnosia would be able to draw an object, to match similar objects and be able to describe the component parts but they would be unable to recognise the objects they had just seen or drawn
• Form agnosia: term for patients who are unable to discriminate between objects and are unable to copy line drawings of objects (apperceptive agnosia)
• Integrative agnosia: refers to patients who can perceive the individual shapes and elements of objects but are unable to integrate these into a representation of the whole object (associative agnosia)

Prosopagnosia: An inability to recognise faces despite adequate visual acuity.

• The fusiform area: has been shown to be a key structure in face and object processing, and numerous studies have shown that the fusiform gyrus contains an area dedicated to face processing called the fusiform face area (FFA). There is variability, however, in the location of this area across individuals.
• Individuation: people with prosopagnosia are less able to recognize one specific item from other members of that class of item
• Many patients with acquired prosopagnosia have bilateral lesions
• Some prosopagnosic patients show evidence of covert recognition, that is, an indication that at some level their brains are discriminating between faces
  • for example: showing differences in neural electrical responses (evoked potentials) produced by viewing familiar and unfamiliar faces
• Congenital prosopagnosia: thought to be present from birth and was traditionally thought to occur without any apparent brain injury
• Developmental prosopagnosia: thought to be a result of early neurological trauma that might be caused by accident or injury

Resources: An Introduction to Cognitive Psychology: Processes and Disorders 3rd edition (Groome, David)