CHAPTER 33 Cognition and 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).
Cognition is the ability to process, retrieve and manipulate information. Cognition for the most part is localized in the frontal lobe of the cerebral cortex (S2.7), however these specific areas interact with many other areas of the brain, making processing highly complex. Emotion is now also considered a cognitive process.
Perception and cognitive functions are essential for efficient interaction with our environment and have been found to have an impact on both movement and posture with impairments noted as a poor prognostic indicator in the population of neurologically impaired patients. The list below shows the hierarchical arrangement of normal perceptual and cognitive processes. Note that the higher levels of the hierarchy depend upon the lower levels as part of their construct:
This incorporates the ability to receive and modulate sensory information and is a prerequisite for perception. Patients with a sensory impairment are therefore likely to experience some perceptual/cognitive problems.
This ability is related to how we become receptive to our sensory environment and allows us to restrict our attention to what is relevant at the present time. This is vital when considering the constant bombardment of our sensory systems. Deficits related to attention are usually associated with damage to the right hemisphere and common presentations include poor attention span and being easily distracted.
Five levels of attention have been identified:
This includes the processing/interpretation of all sensory modalities:
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).
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:
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.
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).
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 |
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).
The detailed assessment of cognitive and perceptual deficits is complex and diagnosis requires a comprehensive assessment carried out by a professional with specialist knowledge. This is usually a clinical psychologist or occupational therapist. However, all neurologically impaired patients should be screened for cognitive/perceptual deficit and therefore the inexperienced therapist should be aware of the possible deficits and how they present.
An understanding of the hierarchy of cognition and perception discussed above will facilitate ideas about simple tasks or specific questions that the therapist could implement in order to test each category. For example, to test the concepts of visuospatial perception, the patient could be asked to place a button in a cup, behind a cup, to the right of a cup. For body schema the patient should be able to point out their own and the therapist’s shoulder, hand and foot. However, caution is advised as many of these processes rely on many sources of information and interact with each other. The therapist should also account for any motor deficits which may influence the patient’s responses.
More severe deficits may be easily discernible, however it may be much harder to identify more subtle problems. The novice therapist should discuss any suspected deficit with a more senior therapist and refer the patient to the relevant professional if the symptom is not being managed.
References and Further Reading
Boyd LA, Winstein CJ. Implicit motor sequence learning in humans following unilateral stroke: the impact of practice and explicit knowledge. Neuroscience Letters. 2001;298:65-69.
Broetz D, Karnath H-O. New aspects for the physiotherapy of pushing behaviour. NeuroRehabilitation. 2005;20:133-138.
Demakis GJ. The neuropsychology of Parkinson’s disease. Disease-a-Month. 2007;533:152-155.
Kandel ER, Schwartz JH, Jessell TM. Principles of neural science, ed 4. New York: McGraw-Hill; 2000.
Karnath H-O. Pusher syndrome: a frequent but little-known disturbance of body orientation perception. Journal of Neurology. 2007;254:415-424.
Multiple Sclerosis Resource Centre. Cognitive problems in MS. www.msrc.co.uk/printablecfm?pageid=1272, 2002.
Parkinson’s Disease Society. The professional’s guide to Parkinson’s disease. www.parkinsons.org.uk/pdf/B126_professionalguidepdf, 2007.
Royal College of Physicians. National Clinical Guidelines for Stroke, ed 2, 2004. Intercollegiate stroke working party. www.rcp.london.ac.uk.
Shumway-Cook A, Woollacott MH. Motor control translating research into clinical practice, ed 3. Philadelphia: Lippincott Williams and Wilkins; 2007.