Cognition and Perception

Published on 03/03/2015 by admin

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Last modified 22/04/2025

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Chapter 33

Cognition and Perception

What are cognition and perception?

Perception

Perception is the organization, integration and interpretation of sensory stimuli (S3.23) to provide meaningful information. Perception may not be a direct record of the environment surrounding us because meaning is constructed by our brains based on learning and previous experience and is therefore highly individual. This complex processing involves many areas of the brain including the sensory association areas of the parietal lobe (S2.7).

Visuospatial neglect is the inability to report, respond or integrate sensory stimuli on the contralateral side of the body to the brain lesion (Shumway-Cook and Woollacott 2007). It is important to understand that this is not a deficit of the visual system but a perceptual impairment usually as a result of right hemisphere lesion (National Clinical Guidelines for Stroke 2004). In its mildest form, the patient may just be inattentive to one side and with instruction/encouragement can scan to the affected side. However, in severe cases, the patient may be completely unaware of any sensory stimuli on the affected side and cannot be encouraged to scan. In this case, the person may be witnessed to only eat food from one half of a plate and will not acknowledge anyone who approaches from the affected side.

Body schema

Body schema is defined as the internal picture which informs our awareness of body parts and their relative position to each other and the environment. It provides a basis for exploration and motor performance. It is continually distributed to networks that plan movement and is updated on a moment by moment basis. A deficit of body schema may result in asomatognosia (the inability to recognize body parts and their relative relationships), visuospatial neglect, left right discrimination or anosognosia (denial of the existence of a disability) (Shumway-Cook and Woollacott 2007). These impairments may lead to problems with mobility and activities of daily living. A further complication is ‘pusher syndrome’.

A pusher resists weight bearing on their non-affected side due to a fear of falling in that direction (Karnath et al 2007). Studies indicate the cause of this syndrome is an altered perception of vertical via the somatosensory systems and ultimately body schema. Interestingly, there appears to be no disturbed processing determining visual vertical (Broetz and Karnath 2005).

Memory

A memory is a specific synchronous pattern of neuronal activity, termed an engram, which occurs as a consequence of learning. Memory involves three stages: encoding, storage and recall, and as such any deficit may result in problems taking on new information or remembering and retrieving learned information. Memories are processed and stored in various regions of the brain and this reflects the existence of different types of memory:

• Sensory memory: This allows us to hold a large amount of information for 1–2 seconds.

• Short-term/working memory: This allows 7 ± 2 bits of information to be held between 30–60 seconds.

• Long-term memory: This potentially has an unlimited capacity and consists of various types of memory:

• Declarative memory stored primarily in the medial temporal lobe in the limbic association areas and comprises:

• Episodic memory of time and place (e.g. what I had for breakfast)

• Semantic memory of general knowledge

• Autobiographical memory: related to our life events.

• Procedural memory: this is our motor memory, often termed implicit memory. Stored in the cerebellum and supplementary and pre motor areas of the frontal lobe.

• Prospective memory: for future events. For example, remembering birthdays.

Recognition

This requires the integration of sensory registration, attention, visual perception and memory to recognize an object, face, etc. and attach meaning. Agnosia is the loss of this ability which may involve recognition of objects, persons, sounds, shapes, or smells.

Praxis

This is the ability to produce skilled purposeful movement. It basically consists of the conceptual ability to organize the task (ideation) and the ability to apply the motor programme correctly (ideomotor). Dyspraxia is a disorder of praxis and is of five types: verbal, facial/oral, limb, constructional and dressing. Dyspraxia is associated with both left and right hemisphere damage, but more commonly with a left sided neurological lesion (National Clinical Guidelines for Stroke 2004; Shumway-Cook and Woollacott 2007).

Limb dyspraxia is defined by two extremes: ideational and ideomotor. However, it is important to note that a continuum exists between the two and patients often present with elements of both conditions. Diagnosis is usually based upon a movement disorder that cannot be explained by any other impairment (e.g. altered tone, sensory loss or incoordination).

Ideational dyspraxia may present with the elements of the task performed in the wrong order; being omitted from the sequence; two or more elements blended together; or with the sequence of actions not completed. The task cannot be performed automatically or with command.

Ideomotor dyspraxia may present as an altered trajectory of movement; poor distance judgement; gestural enhancement; perseveration; vocal overflow; or with a body part being used as an object. The task can be performed automatically but not on command.

Higher executive function

This function includes planning, organization, problem-solving, self-initiation, self-monitoring and self-inhibition of behaviour, and is associated with the frontal lobes of the cerebral cortex (S2.7). The ability to learn is also a cognitive skill and therapists rely heavily on both implicit (during motor learning) and explicit learning (when giving instructions) in rehabilitation. A deficit of these higher level cognitive skills is often termed dysexecutive syndrome and may include the behaviours indicated in Table 33.1.

Table 33.1

Behaviours associated with dysexecutive syndrome

Executive skill	Abnormal behaviour
Initiation drive	Apathy and unable to initiate behaviour
Response inhibition	Impulsive and over responsive. Perseveration
Task persistence	Unable to maintain attention
Organize actions and thoughts	Problems identifying goals and planning behaviour
Generative thinking	Rigid and narrow thinking. Limited creativity and flexibility
Awareness of own behaviour	Difficulty modifying behaviour. Limited insight into actions, feelings and deficits

Why do I need to consider cognition and perception?

In pathologies that may affect the cerebral cortex and higher centres, cognitive and perceptual deficits are common and potentially as debilitating as any physical symptom.

The incidence in Parkinson’s disease (PD) is high, although not viewed as a primary symptom of the disease. Dysexecutive syndrome (Demakis 2007), visuospatial dysfunction and change in memory and mood (The Parkinson’s Disease Society 2007) have been reported in early PD, with long-term survivors likely to develop dementia.

The incidence in multiple sclerosis (MS) is reported as 50–80% (MS Resource Centre 2002), with the most common symptoms being mild problems with memory, attention span and the speed of processing information. Factors that exacerbate these deficits include low mood and depression, stress, heat and fatigue.

The incidence in cerebrovascular accident (CVA) is also high and commonly constitutes a lack of spatial awareness, poor attention span and problems with memory and higher executive function (National Clinical Guidelines for Stroke 2004).