Assessment and intervention of perceptual dysfunction
Perception is the mechanism by which the brain interprets sensory information received from the environment. The perceived information is then further processed by the various cognitive functions, and the individual may choose either to respond with a verbal expression or motor act, or to simply perceive and think about the observed stimuli.
In early development, tactile, proprioceptive, vestibular, and visual perception provide an internalized sense of the body scheme, which is basic to all motor function. The process of interpreting visual input is a learned skill, as evidence by blind individual who, when sight is restored later in life, have difficulty making sense of what they see.
Severe perceptual deficits, frequently combined with cognitive impairments, can affect every area of occupation and can serious safety concerns.
General Principles of the OT Assessment
When assessing perceptual abilities several assessment tools may be required. With a variety of such tests, the therapist can gather information to discriminate between a deficit in the reception of information and a deficit in the verbal or motor output. This, in turn, influences the intervention approach. Observation of occupational performance and analysis of the perceptual-motor demands of functional activities further complement standardized assessment tools and enable the determination of underlying causes of deficits in occupational performance. Assessment methods should be conducted in the specific context of the occupation being performed.
General Approaches to OT Intervention
An underlying assumption about perceptual-motor function is that perceptual deficits will adversely affect occupational performance. Further, it is assumed that remediation of or compensation for perceptual deficits will improve occupational performance. In her critical analysis of approaches to treatment for perceptual deficits, Neistadt (1990) described two general classifications of approaches: the adaptive and remedial. Adaptive approaches provide training in daily living behaviors to facilitate adaptation to the client’s unique contextual environment. In contrast, the remedial approaches seek to cause some change in central nervous system (CNS) functions. The effectiveness of the various approaches to the remediation of perceptual deficits has not been well documented and requires further scientific investigation.
A therapist may use one approach or a combination of approaches when designing an intervention plan to address the effects of perceptual dysfunction. The remedial and adaptive approaches can used in a continuum, beginning with attempts to improve the basic skills and gradually incorporating compensatory techniques as the deficit persist.
Remedial, or transfer of training, approaches assume that practice in a particular perceptual task carries over to performance of similar activities or tasks requiring the same perceptual skills.
Adaptive, or function, approaches are characterized by the repetitive practice of particular tasks that help the person become more independent in areas of occupation. The therapist does not retrain specific perceptual skills. Rather, the person is made aware of the problem and taught methods of adapting to or compensating for the deficit dueing occupational performance.
Assessment and Intervention of Specific Perceptual Impairments
Visual Perception Disorders
Visual object recognition refers to the ability to identify objects via visual input. An impairment in this area is called agnosia, and is caused by lesions in the right occipital lobe or posterior multimodal area. The individual with agnosia demonstrates normal visual foundation skills, as indicated by the person’s ability to ambulate around furniture through a room; further, the inability to name objects is not caused by a language deficit in naming the object, as noted in aphasic disorders. Rather, the person is unable to recognize and identify an item using only visual means. If the person holds the object, he or she can identify it via tactile input, or by olfactory means if the object has a distinguishable odor.
Assessment is performed by asking the individual to identify five common objects by sight. If the client demonstrates word-finding difficulties, offer the client a choice of three answers. Ask the client to indicate the correct choice through a head nod (“yes” or “no”). If the client is unable to name four out of the five objects, visual agnosia may be indicated.
OT intervention for visual agnosia will focus on adaptive or compensatory methods of keeping frequently used objects in consitent locations, and teaching the client to rely more heavily on intact sensory modalities to seek and find desired itemsv. Remediation approaches can include having the client practice identifying objects that are needed for occupational performance or using nonverbal, tactile-kinesthetic guiding during occupations. Following the activity, have the client practice naming the items that were used.
Color Agnosia and Color Anomia
Color agnosia refers to the client’s inability to remember and recognize the specific colors for common objects in the environment[iii]. Alternatively, color anomia refers to the client’s inability to name the color of the objects. While the client understands the differences between the different of colors of object, they are unable to name the object accurately.
To assess color agnosia, present the client with two common objects that are accurately colored and two common objects that are not accurately colored. Ask the client to pick out those common objects that are not accurately colored. If the client is unable to choose the objects that are inaccurately colored, color agnosia may be indicate.
To assess color anomia, ask the client to name the color of various objects in their environmen. If the patient has aphasia, ask them to nod their head “yes” or “no” after offering them choices of colors. If the client is unable to correctly name the colors of various objects, color anomia may be indicated.
OT intervention for color agnosia and color anomia will focus on providing the client with opportunities to recognize, identify, and name various colors of objects in their environment. Intervention is best provided in a familiar context and can be incorporated functionally during occupational performance.
Metamorphosia refers to the visual distortion of objects, such as the physical properties of size and weight.
Assessment for metamorphosia includes presenting the client with various objects of different weights and sizes. Ask the client to place each object in order according to size or weight through observation alone. Metamorphosia may be indicated if the client is unable to determine the weight and size of the various objects.
OT intervention for metamorphosia includes providing the client with opportunities to practice distinguishing objects in the natural environment through intact sensory modalitise. The functional use of objects during occupational performance will provide feedback to the client about the sizes and shapes of different objects. The therapist should also provide specific verbal descriptors of the object when using this approach.
Prosopagnosia refers to an inability to recognize and identify familiar faces caused by lesions of the right posterior hemisphere. The individual with prosopagnosia may have difficulty recognizing his or her own face, faces of family members and friends, and/or of famous individuals because they cannot recognize the unique facial expressions that make each face different. When attempting to identify family members and acquaintances, the person tends to compensate by relying on auditory or a distinctive feature.
Brain lesions can also impair the ability to interpret facial expressions, which can have significant social consequences.
Informal functional assessments could include having the client identify the names of the people in photographs or by having the client identify his or her own face in a mirror. Photographs of famous people could also be used. If aphasia is present, have the client communicate through gestures. If the client is unable to identify self or family members, prosopagnosia may be indicated.
OT interventions for prosopagnosia include remedial approaches such as providing face matching exercisesviii. Adaptive approaches include providing pictures of family members and famous people with names and assisting the client to associate the family member’s face with other characteristics and features.
Simultagnosia refers to the inability to recognize and interpret a visual array as a whole, and is caused by lesions to the right hemisphere of the brain. Clients with simultanognosia are able to identify the individual components of visual components, but are unable to recognize and interpret the gestalt of the scene.
Assessment includes presenting the client a photograph of a detailed visual array, asking the client to describe the scene in detail, and assessing whether or not the client can describe the scene as a whole. Many clients will be able to identify specific features of the visual array, but cannot desribe the context or meaning of the whole scene. Simultanogsia is indicated when the client cannot recognize and interpret a visual array as a whole.
OT intervention will focus on assisting the client to construct meaning of a visual array through verbal cues and therapeutic questions to facilitate abstract reasoning. Intervention is best provided in familiar contexts.
Visual-Spatial Perception Disorders
Visual-spatial perception refers to capacity to appreciate the spatial arragement of one’s body, objects in relationship to oneself, and relationship between objects in space. It is generally acknowledged that the right hemisphere, which controls spatial abilities, tends to function in the gestalt (whole), whereas the left hemisphere, which is responsible for linguistic operations, tends to focus on discrete details.
Visual-spatial perception often occurs instaneously, and it is because of this rapid processing of information. An individual with mild visual-spatial impairment may need addition time to perform a task, but processes the information correctly, possibly by compensating with verbal analysis of the perceptual components. Severe impairment may result in the incorrect response despite additional time used in attempting to solve the problem.
Visual-spatial skills are not limited to the visual domain. Sound can be localized in space, and the mobility and daily occupations of blind individuals are heavily dependent on the tactile appreciation of the spatial arragements of objects.
Figure-Ground Discrimination Dysfunction
Figure-ground discrimination allows a person to perceive the foreground from the background in a visual array.
Figure-ground discrimination can be assessed functionally in a variety of contexts. Figure-ground discrimination dysfunction may be indicated if the client is uanble to discriminate the foreground from the background in a complex visual array.
Using a remedial approach, intervention for figure-ground discrimination dysfunction should focus on challenging the client to localize objects of similar color in a disorganized visual array. The task could be incorporated contextually into meaningful occupation.
An adaptive approach to intervention would focus on modifyinmg the environment to increase the organization of common functional objects, decreasing the complexity of visual array that the client has to discriminate, or marking common objects with colored tape so that objects are easily distinguished from one another, particularly when the objects are of a similar color.
Form constancy is the recognition of various forms, shapes, and objects, regardless of their position, location, or size.
To assess form constancy, ask the client to identify familiar objects in their environment through observation alone when those objects are placed upside down or on their side. Form-constancy dysfunction may be indicated if the client is unable to identify objects in a position that from the norm.
Intervention for form-constancy dysfunction would include using tactile cues to feel objects in various positions so that the client learns the constancy of them despite their position, size, or location. Activity can be graded from positioning all objects in an upright position to placing objects in odd position. Intervention is best provided with common object objects that the client utilities in everyday occupational performance.
Position in Space
Position in space, or spatial relations, refers to the relative orientation of a shape or object to the self.
To assess position in space, have the client place common objects in relation to the self or other objects using the following directional terms: top/bottom, up/down, in/out, behind/ in front of, and before/after. Position in space dysfunction may be indicated if the client is unable to discern the relationships of objects to the self or other objects through directional terms.
Intervention for position in space includes providing the client with opportunities to experience the organiztion of objects in the environment to the self.
Right-Left Discrimination Dysfunction
Right-left discrimination is the ability to accurately use the concepts of right and left. An individual with right-left discrimination dysfunction may confuse the right and left side of his or her body or confuse right and left in directional terms when navigating through their environment.
To assess right-left discrimination, ask the client to point to various body parts or assess the client’s ability to accurately navigate their environment through verbal commands using right and left. Right-left discrimination dysfunction may be indicated if the client is unable to differentiate between right and left in relation to their body and their environment.
Intervention for right-left discrimination will focus on assisting the client to practice reciting right and left as they are interacting with their own body or their environment. Remediation of right-left discrimination can significantly improve topographical orientation as the client learns to navigate in a more dynamic home and community environment.
Stereopsis is the inability to perceive depth in relation to the self or in relation to various objects in the environment. Depth perception is critical to function in a three-dimensionaal world and to safety in driving and community mobility.
To assess depth perception, place a variety of common objects on a table surface and ask the client to identify which object is closer and farther away. In community context, the client may also be assessed functionally by asking him or her to idenify building or landmarks that are closer or farther away. Stereopsis may be indicated if the client is unable to judge the distance between objects in the environment.
Tactile Perception Disorders
Stereognosis, also known as tactile gnosis, is the perceptual skill that enables an individual to identify common objects and geometric shapes through tactile perception without the aid of vision. It result from the integration of the sense of touch, pressure, position, motion, texture, weight, and temperature and is dependent on intact parietal cortical function. Stereognosis is essential to occupational performance because the ability “to see with the hands” is critical to many daily activities. Along with proprioception, stereognosis enables the use of all hand tools and performance of hand activities without the need to concentrate visually on the implements being used. A deficit in stereognosis is called astereognosis. Persons who have astereognosis but retain much of their motor function must visually monitor their hands’ activities. Thus, they msut be very slow and purposeful in their movements and tend to be generally less active.
The purpose of a stereognosis test is to assess a client’s ability to identify common objects and perceive their tactile properties. Any common objects may be used, but it is important to consider the client’s social and ethnic background to ensure that he or she has had previous experience with the objects. Three-dimensional geometric shapes can also be used to test shape and form perception.
The test should be conducted in privacy in an environment with minimal distractions. The client should be seated at a table in a position that accomodates the affected hand and forearm comfortably. The therapist should sit opposite the person being tested. If thw client is unable to manipulate test objects because of motor weakness, the therapist should assist him or her to manipulate them in as near normal s manner as possible. The client’s vision is occluded, with the dorsal surface of the hand resting on the table. Objects are presented in random order. Manipulation of objects is allowed and encouraged. The therapist assist with the manipulation of items if the person’s hand function is impaired. The client should be asked to name the object, to describe its properties. Clients with aphasia may view a duplicate set of test objects after each trial and point to a choice. The person’s response to each of the items presented is scored. The therapist notes if the object is identified quickly and correctly, if there is a long delay before the identification of the object, or if the individual can describe only properties of the object. The therapist also notes if the person cannot identify the object or describe its properties.
An additional test of tactile perception that measure parietal lobe function is the test for graphesthesia, the ability to recognize numbers, letters, and forms written on the skin. The loss of this ability is called agraphesthesia. To test agraphesthesia, the examiner occludes the client’s vision and traces letters, numbers, or geometric formson the fingertips or palm with a dull-pointed pencil or similar instrument. The client tells the therapist which symbol was written. If the client has aphasia, pictures of the symbols may be provided for the individual to indicate a response after each test stimulus. Agraphesthesia is indicated if the client unable to state or identify the symbol written on the palm.
OT intervention for agraphesthesia will focus on providing the client with opportunities for tactile discrimination through the use of the hands. The therapist can grade the intervention from tracing letters and numbers to words and geometric forms on the palm of the hand. With their vision occluded, the client can also practice writing their name in their opposite palm.
Body Schema Perception Disorders
Following a CVA or TBI, a person’s sense of his or her body’s shape, position, and capacity frequently is distorted. This is known as a disorder of body schema, or autotopagnosia. This can be noted in attempts to draw a human figure or in a person’s unrealistic expectations of performance abilities. The disorder can affect egocentric perception of one’s own body or allocentric orientation of another person’s body. A person’ may neglect one side of the body or demonstrate generally distorted impressions of the body’s configuration. The person may confuse his or her body with that of another. Finger agnosia, or the inability to discriminate the fingers of the hand, can also be part of the disorder. An impaired body scheme will also affect participation in occupation and performance skills.
Body schema perception disorders can be assessed by asking the individual to draw a human figure or point to body parts on command. Finger agnosia is evaluated by occluding the person’s vision and asking him or her to name each finger as it is touched by the therapist. Unilateral body neglect can be observed functionally during occupational performance as the client ignores the affected limb and/or states that a body part is not his or her own. A body schema perception disorder may indicated if the client is unable to correctly identify parts of his or her body.
A remedial approach to intervetion for body schema perception disorders should focus on providing the client with opportunities to reinforce body knowledge through tactile and proprioceptive stimulation. As the client incorporates the use of their affected limb into occupational performance, the client will begin to gain perceptual awareness of their body and the relationship of various body parts.
Motor Perception Disorders
Praxis is the ability to plan and perform purposeful movement. Apraxia has been classically defined as a deficit in the execution of learned movement, which cannot be accounted for by either weakness, incoordination, or sensory loss, or by incomprehension of or inattention of commands. The disorder can result from damage to either side of brain or to corpus callosum but is more frequently noted with left hemisphere damage. Apraxia is often seen in persons with aphasia; however, not all aphasic person are apraxic, nor are all apraxic persons aphasic.
Ideational apraxia is a conceptual deficit, seen as an inablity to use real objects appropriately. The individual also may have difficulty sequencing acts in the proper order. The individual may use the wrong tool with for the task or may associate the wrong object to be acted . This deficit has significant functional implications in a variety of areas occupation.
Ideomotor apraxia is an inability to carry out a motor act on verbal command or imitation. However, the person with ideomeotor apraxia is able to perform the act correctly when asked to use the actual object. Observation of the person in areas of occupation is critical to the identification of ideomotor apraxia. Impairments are demonstrated only in the testing environment and appear to have little functional impact, ascompared with ideational apraxia.
Another category of motor perception disorders seen in the literature is dressing apraxia. The classification of dressing impairment as a form of apraxia has been questioned in recent years because the difficulties in ADLs are considered to be caused by perceptual or cognitive dysfunction, or are seen as an extension of an ideational or ideomotor apraxic disorder.
General Principles in the Assessment and Treatment of Apraxia
It is important that assessment of sensory function, muscle strength, and dexterity are completed before the test of praxis because deficits in these areas would complicate any assessment of apraxia. If a person has a hemiplegia, the unaffected hand is used for testing.
A thorough assessment includes items presented and involves both transitive movement (action involving both tool and use) and intransitive movements (movements for communication).
The term constructional disorder is now favored over the previously used term of two- and three-dimensional constructional apraxia since the deficit does not clearly fall within the definition of apraxia. Many occupations depend on visuoconstructional skills, or the ability to organize visual information into meaningful spatial representations. Constructional deficits refer to the inability to organize or assemble parts into a whole. Constructional deficits can result in significant dysfunction in occupations that require constructional ability. An individual acts on his or her contextual environment based on the information he or she perceives. Therefore, deficits in perception become more apparent when a person interacts with the environment in maladaptive ways.
In daily living, occupations require constructional skills. To perform tasks successfully, an individual must have integrated visual perception, motor planning, and motor execution.
The remedial approach to intervention involves the use of perceptual tasks to improve contructional skills. The adaptive approach would include participation in occupational performance and developing compensatory approaches to the functional performance skill deficits.
Behavioral Aspects of Perceptual Dysfunction
Some degree of accurate self-awareness and recognition of the effect of the disability on one’s functioning is needed if the person is to invest energy in the therapy process. An individual who is unaware of perceptual deficits may be a serious safety risk and may attempt occupations that are well beyond present physical abilities. A person’s innate trust of accuracy of perceptions often is a basis for unrealistic self-confidence; demonstrating to the individual that his or her perceptions are now distorted and no longer trustworthy can profoundly affect the person’s sense of self. A therapist needs to respect and be sensitive to the individual’s sense of self and be prepared to aid the client in understanding the changes in perceptual capacity and in re-establishing an accurate sense of self-awareness.
An individual who has some degree of awareness of the disability often is depressed, which seems an appropriate response to the gravity of the situation. The therapist needs to recognize and appreciate this emotional response and help the person achieve an emotional balance to re-establish quality of life through celebrating progress in therapy while aknowledging the impact of the disability.