Associative visual agnosia

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Associative visual agnosia
Lobes of the brain.jpg
Inferior view of the brain, depicting the cerebral lobes. Lesions on the occipito-temporal lobes are correlated with associative agnosia.

Associative visual agnosia is a form of visual agnosia. It is an impairment in recognition or assigning meaning to a stimulus that is accurately perceived and not associated with a generalized deficit in intelligence, memory, language or attention. [1] The disorder appears to be very uncommon in a "pure" or uncomplicated form and is usually accompanied by other complex neuropsychological problems due to the nature of the etiology. [1] Affected individuals can accurately distinguish the object, as demonstrated by the ability to draw a picture of it or categorize accurately, yet they are unable to identify the object, its features or its functions.

Contents

Classification

Agnosias are sensory modality specific, usually classified as visual, auditory, or tactile. [2] [3] Associative visual agnosia refers to a subtype of visual agnosia, which was labeled by Lissauer (1890), as an inability to connect the visual percept (mental representation of something being perceived through the senses) with its related semantic information stored in memory, such as, its name, use, and description. [4] [5] [6] This is distinguished from the visual apperceptive form of visual agnosia, apperceptive visual agnosia , which is an inability to produce a complete percept, and is associated with a failure in higher order perceptual processing where feature integration is impaired, though individual features can be distinguished. [7] In reality, patients often fall between both distinctions, with some degree of perceptual disturbances exhibited in most cases, and in some cases, patients may be labeled as integrative agnostics when they fit the criteria for both forms. [1] Associative visual agnosias are often category-specific, where recognition of particular categories of items are differentially impaired, which can affect selective classes of stimuli, larger generalized groups or multiple intersecting categories. For example, deficits in recognizing stimuli can be as specific as familiar human faces or as diffuse as living things or non-living things. [7]

An agnosia that affects hearing, auditory sound agnosia , is broken into subdivisions based on level of processing impaired, and a semantic-associative form is investigated within the auditory agnosias. [2]

Causes

Associative visual agnosias are generally attributed to anterior left temporal lobe infarction (at the left inferior temporal gyrus), [8] caused by ischemic stroke, head injury, cardiac arrest, brain tumour, brain hemorrhage, or demyelination. [7] [9] Environmental toxins and pathogens have also been implicated, such as, carbon monoxide poisoning or herpes encephalitis and infrequent developmental occurrences have been documented. [1] [10]

The separate streams of the visual processing system. The ventral "what" stream is in purple and the dorsal "where" stream is in green. Ventral-dorsal streams.svg
The separate streams of the visual processing system. The ventral "what" stream is in purple and the dorsal "where" stream is in green.

Most cases have injury to the occipital and temporal lobes and the critical site of injury appears to be in the left occipito-temporal region, often with involvement of the splenium of the corpus callosum. [11] The etiology of the cognitive impairment, as well the areas of the brain affected by lesions and stage of recovery are the primary determinants of the pattern of deficit. [1] More generalized recognition impairments, such as, animate object deficits, are associated with diffuse hypoxic damage, like carbon monoxide poisoning; more selective deficits are correlated with more isolated damage due to focal stroke. [1]

Damage to the left hemisphere of the brain has been explicitly implicated in the associative form of visual agnosia. [12] [13] Goldberg suggested that the associative visual form of agnosia results from damage to the ventral stream of the brain, the occipito-temporal stream, which plays a key role in object recognition as the so-called "what" region of the brain, as opposed to the "where," dorsal stream. [12]

Theoretical explanations

Teuber [14] described the associative agnostic as having a "percept stripped of its meaning," because the affected individual cannot generate unique semantic information to identify the percept, since though it is fully formed, it fails to activate the semantic memory associated with the stimulus. [8] Warrington (1975) [15] offered that the problem lies in impaired access to generic engrams (memory traces) that describe categories of objects made up of a multitude of similar elements. [12] Essentially, damage to a modality-specific meaning process (semantic system), is proposed, either in terms of defective access to or a degradation of semantic memory store for visual semantic representations themselves. [13] [16] The fact that agnosias are often restricted to impairments of particular types of stimuli, within distinct sensory modalities, suggests that there are separate modality specific pathways for the meaningful representation of objects and pictures, written material, familiar faces, and colors. [17]

Object recognition model

Depiction of the object recognition model, adapted from Bauer's Clinical Application of a Cognitive Neuropsychological Model of Object Recognition Object Recognition Model.png
Depiction of the object recognition model, adapted from Bauer's Clinical Application of a Cognitive Neuropsychological Model of Object Recognition

Cognitive psychology often conceptualizes this deficit as an impairment in the object recognition process. Currently visual agnosias are commonly explained in terms of cognitive models of object recognition or identification. [9] The cognitive system for visual object identification is a hierarchal process, broken up into multiple steps of processing. [16]

In the object recognition unit model by Marr (1980), [18] the process begins with sensory perception (vision) of the object, which results in an initial representation via feature extraction of basic forms and shapes. This is followed by an integration stage, where elements of the visual field combine to form a visual percept image, the 'primary sketch'. This is a 2+1⁄2 dimensional (2+1⁄2D) stage with a 'viewer-centered' object representation, where the features and qualities of the object are presented from the viewer's perspective. [5] The next stage is formation of a 3 dimensional (3D) 'object-centered' object representation, where the object's features and qualities are independent of any particular perspective. Impairment at this stage would be consistent with apperceptive agnosia. [1] This fully formed percept then triggers activation of stored structural object knowledge for familiar things. [9] This stage is referred to as "object recognition units" and distinctions between apperceptive and associative forms can be made based on presentation of a defect before or after this stage, respectively. [16] This is the level at which one is proposed to perceive familiarity toward an object, which activates the semantic memory system, containing meaning information for objects, as well as descriptive information about individual items and object classes. The semantic system can then trigger name retrieval for the objects. A patient who is not impaired up until the level of naming, retaining access to meaning information, are distinguished from agnostics and labeled as anomic. [1]

Non-abstracted view

In an alternate model of object recognition by Carbonnel et al. [19] episodic and semantic memory arise from the same memory traces, and no semantic representations are stored permanently in memory. By this view, the meaning of any stimulus emerges momentarily from reactivation of one's previous experiences with that entity. Each episode is made of several components of many different sensory modalities that are typically engaged during interactions with an object. In this scenario, a retrieval cue triggers reactivation of all episodic memory traces, in proportion to the similarity between the cue its 'echo,' the components shared by most activated traces. In a process called 're-injection,' the first echo acts as a further retrieval cue, evoking the 'second echo,' the less frequently associated components of the cue. Thus, the 're-injection' process provides a more complete meaning for the object. According to this model, different types of stimuli will evoke differential 'echos' based on typical interactions with them. [9] For example, a distinction is made between functional and visual components of various stimuli, such that impairment to these aspects of the memory trace will inhibit the re-injection process needed to complete the object representation. This theory has been used to explain category-specific agnosias that impair recognition of various object types, such as animals and words, to different degrees. [9]

Common forms of visual associative agnosia

DisorderRecognition impairmentRetained abilitiesLocation of lesion
Visual object agnosiaOften specific to a particular category or categories of stimuli, i.e. living/animate things, tools, musical instruments, etc.
  • Images can be copied, demonstrating intact object perception
  • Objects usually identifiable by sensory modalities other than vision [20]
Bilateral occipito-temporal cortex [11]
Associative prosopagnosia Familiar faces
  • In associative form, can match and discriminate between unrecognized faces based on facial features [16]
Usually bilateral, sometimes right unilateral, inferior occipital and posterolateral temporal cortex [11]
Pure alexia Written words
  • Comprehension of verbal speech, shows intact word knowledge
  • Words can be copied, shows intact perception of words [20]
Left occipital lobe and related fibers connecting right and left hemispheres in subjacent white matter or splenium [11]
Cerebral achromatopsia Color associations
  • Can discriminate between and match shades of color, therefore hue perception intact
Bilateral or left unilateral occipito-temporal cortex [16]
Topographical disorientation Familiar places
  • Can describe layouts of buildings or spaces, therefore topographical memory retained
Right posterior cingulate cortex

Visual object agnosia

Visual object agnosia (or semantic agnosia) is the most commonly encountered form of agnosia. [16] The clinical "definition" of the disorder is when an affected person is able to copy/draw things that they cannot recognize. Individuals often cannot identify, describe or mimic functions of items, though perception is intact, since images of objects can be copied or drawn. [7] Individuals may retain semantic knowledge of the items, as exemplified during tasks where objects are presented through alternate modalities, through touch or verbal naming or description. Some associative visual object agnostics retain the ability to categorize items by context or general category, though unable to name or describe them. [16] Diffuse hypoxic damage is the most common cause of visual object agnosias. [8]

Category-specific agnosia

Category-specific agnosias are differential impairments in subject knowledge or recognition abilities pertaining to specific classes of stimuli, such as living things vs. non-living things, animate vs. inanimate things, food, metals, musical instruments, etc. Some of the most common category-specific agnosias involve recognition impairments for living things, but not non-living things, or human faces, as in prosopagnosia. This type of deficit is typically associated with head injury or stroke, though other medical conditions have been implicated, such as, herpes encephalitis. [2]

Prosopagnosia

Prosopagnosia (or "face blindness") is a category-specific visual object agnosia, specifically, impairment in visual recognition of familiar faces, such as close friends, family, husbands, wives, and sometimes even their own faces. Individuals are often able to identify others through alternate characteristics, such as, voice, gait, context or unique facial features. This deficit is typically assessed through picture identification tasks of famous persons. This condition is associated with damage to the medial occipito-temporal gyri, including the fusiform and lingual gryi, as the suggested location of the brain's face recognition units. [7] [11] [16]

Associative and apperceptive forms

Two subtypes are distinguished behaviorally as being associative or apperceptive in nature. Associative prosopagnosia is characterized by an impairment in recognition of a familiar face as familiar; however, individuals retain the ability to distinguish between faces based on general features, such as, age, gender and emotional expression. [20] This subtype is distinguished through facial matching tasks or feature identification tasks of unknown faces. [16]

Pure alexia

Pure alexia ("alexia without dysgraphia" or "pure word blindness") is a category-specific agnosia, characterized by a distinct impairment in reading words, despite intact comprehension for verbally presented words, demonstrating retained semantic knowledge of words. [7] [20] Perceptual abilities are also intact, as assessed by word-copying tasks. [2]

Cerebral achromatopsia

Color agnostics fail to identify abnormally colored objects or pictures Banana-fluorescence-081108.jpg
Color agnostics fail to identify abnormally colored objects or pictures

Cerebral achromatopsia, also known as Color agnosia, is a category-specific semantic impairment pertaining to semantic color associations, such that individuals retain perceptual abilities for distinguishing color, demonstrated through color categorization or hue perception tasks; however knowledge of typical color-object relationships is defective. [7] [8] [16] Color agnostics are assessed on performance coloring in black and white images of common items or identifying abnormally colored objects within a set of images. [2] For example, a color agnostic may not identify a blue banana as being improperly colored.[ citation needed ]

Overlap with color anomia

This deficit should be distinguished from color anomia, where semantic information about color is retained, but the name of a color cannot be retrieved, though co-occurrence is common. Both disorders linked to damage in the occipito-temporal cortex, especially in the left hemisphere, which is believed to play a significant role in color memory. [16]

Diagnosis

A recognition disorder is not considered to be agnosia unless there is a lack of aphasia, dementia, or other generalized defect that affects any stage of the object recognition process, such as, deficiencies in intelligence, linguistic ability, memory, attention or sensory perception. [1] [2] Therefore, individuals must be assessed for language ability, auditory comprehension, fluency, repetition, praxis, and reading and writing.

A Flowchart for Clinical Assessment of Forms of Visual Agnosia Flowchart for Assessment of Visual Agnosias.png
A Flowchart for Clinical Assessment of Forms of Visual Agnosia

Goals of clinical assessment of agnosia

  1. Ruling out alternative conditions leading to the recognition impairment, such as, primary sensory disruption, dementia, aphasia, anomia, or unfamiliarity with the object category or elements.
  2. Determination of the scope and specific nature of the recognition impairment. Including:
  • Specific sensory modality
  • Specific category of stimuli
  • Specific conditions under which recognition is possible [1]

Testing

Specialists, like ophthalmologists or audiologists, can test for perceptual abilities. Detailed testing is conducted, using specially formulated assessment materials, and referrals to neurological specialists is recommended to support a diagnosis via brain imaging or recording techniques. The separate stages of information processing in the object recognition model are often used to localize the processing level of the deficit. [1]

Testing usually consists of object identification and perception tasks including:

Overlap with optic aphasia

Sensory modality testing allows practitioners to assess for generalized versus specific deficits, distinguishing visual agnosias from optic aphasia, which is a more generalized deficit in semantic knowledge for objects that spans multiple sensory modalities, indicating an impairment in the semantic representations themselves. [13]

Apperceptive vs. associative

The distinction between visual agnosias can be assessed based on the individual's ability to copy simple line drawings, figure contour tracking, and figure matching. [5] Apperceptive visual agnostics fail at these tasks, while associative visual agnostics are able to perform normally, though their copying of images or words is often slavish, lacking originality or personal interpretation. [1]

Treatment

The affected individual may not realize that they have a visual problem and may complain of becoming "clumsy" or "muddled" when performing familiar tasks such as setting the table or simple DIY. Anosognosia, a lack of awareness of the deficit, is common and can cause therapeutic resistance. [2] In some agnosias, such as prosopagnosia, awareness of the deficit is often present; however shame and embarrassment regarding the symptoms can be a barrier in admission of a deficiency. [16] Because agnosias result from brain lesions, no direct treatment for them currently exists, and intervention is aimed at utilization of coping strategies by patients and those around them. Sensory compensation can also develop after one modality is impaired in agnostics [1]

General principles of treatment:

Partial remediation is more likely in cases with traumatic/vascular lesions, where more focal damage occurs, than in cases where the deficit arises out of anoxic brain damage, which typically results in more diffuse damage and multiple cognitive impairments. [2] However, even with forms of compensation, some affected individuals may no longer be able to fulfill the requirements of their occupation or perform common tasks, such as, eating or navigating. Agnostics are likely to become more dependent on others and to experience significant changes to their lifestyle, which can lead to depression or adjustment disorders. [1]

Related Research Articles

<span class="mw-page-title-main">Agnosia</span> Medical condition

Agnosia is the inability to process sensory information. Often there is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss. It is usually associated with brain injury or neurological illness, particularly after damage to the occipitotemporal border, which is part of the ventral stream. Agnosia only affects a single modality, such as vision or hearing. More recently, a top-down interruption is considered to cause the disturbance of handling perceptual information.

<span class="mw-page-title-main">Temporal lobe</span> One of the four lobes of the mammalian brain

The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.

<span class="mw-page-title-main">Prosopagnosia</span> Cognitive disorder of face perception

Prosopagnosia, also known as face blindness, is a cognitive disorder of face perception in which the ability to recognize familiar faces, including one's own face (self-recognition), is impaired, while other aspects of visual processing and intellectual functioning remain intact. The term originally referred to a condition following acute brain damage, but a congenital or developmental form of the disorder also exists, with a prevalence of 2.5%. The brain area usually associated with prosopagnosia is the fusiform gyrus, which activates specifically in response to faces. The functionality of the fusiform gyrus allows most people to recognize faces in more detail than they do similarly complex inanimate objects. For those with prosopagnosia, the method for recognizing faces depends on the less sensitive object-recognition system. The right hemisphere fusiform gyrus is more often involved in familiar face recognition than the left. It remains unclear whether the fusiform gyrus is specific for the recognition of human faces or if it is also involved in highly trained visual stimuli.

Semantic memory refers to general world knowledge that humans have accumulated throughout their lives. This general knowledge is intertwined in experience and dependent on culture. New concepts are learned by applying knowledge learned from things in the past.

Astereognosis is the inability to identify an object by active touch of the hands without other sensory input, such as visual or sensory information. An individual with astereognosis is unable to identify objects by handling them, despite intact elementary tactile, proprioceptive, and thermal sensation. With the absence of vision, an individual with astereognosis is unable to identify what is placed in their hand based on cues such as texture, size, spatial properties, and temperature. As opposed to agnosia, when the object is observed visually, one should be able to successfully identify the object.

<span class="mw-page-title-main">Visual memory</span> Ability to process visual and spatial information

Visual memory describes the relationship between perceptual processing and the encoding, storage and retrieval of the resulting neural representations. Visual memory occurs over a broad time range spanning from eye movements to years in order to visually navigate to a previously visited location. Visual memory is a form of memory which preserves some characteristics of our senses pertaining to visual experience. We are able to place in memory visual information which resembles objects, places, animals or people in a mental image. The experience of visual memory is also referred to as the mind's eye through which we can retrieve from our memory a mental image of original objects, places, animals or people. Visual memory is one of several cognitive systems, which are all interconnected parts that combine to form the human memory. Types of palinopsia, the persistence or recurrence of a visual image after the stimulus has been removed, is a dysfunction of visual memory.

Simultanagnosia is a rare neurological disorder characterized by the inability of an individual to perceive more than a single object at a time. This type of visual attention problem is one of three major components of Bálint's syndrome, an uncommon and incompletely understood variety of severe neuropsychological impairments involving space representation. The term "simultanagnosia" was first coined in 1924 by Wolpert to describe a condition where the affected individual could see individual details of a complex scene but failed to grasp the overall meaning of the image.

Semantic dementia (SD), also known as semantic variant primary progressive aphasia (svPPA), is a progressive neurodegenerative disorder characterized by loss of semantic memory in both the verbal and non-verbal domains. However, the most common presenting symptoms are in the verbal domain. Semantic dementia is a disorder of semantic memory that causes patients to lose the ability to match words or images to their meanings. However, it is fairly rare for patients with semantic dementia to develop category specific impairments, though there have been documented cases of it occurring. Typically, a more generalized semantic impairment results from dimmed semantic representations in the brain.

Visual agnosia is an impairment in recognition of visually presented objects. It is not due to a deficit in vision, language, memory, or intellect. While cortical blindness results from lesions to primary visual cortex, visual agnosia is often due to damage to more anterior cortex such as the posterior occipital and/or temporal lobe(s) in the brain.[2] There are two types of visual agnosia: apperceptive agnosia and associative agnosia.

<span class="mw-page-title-main">Inferior temporal gyrus</span> One of three gyri of the temporal lobe of the brain

The inferior temporal gyrus is one of three gyri of the temporal lobe and is located below the middle temporal gyrus, connected behind with the inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface of the temporal lobe, where it is limited by the inferior sulcus. This region is one of the higher levels of the ventral stream of visual processing, associated with the representation of objects, places, faces, and colors. It may also be involved in face perception, and in the recognition of numbers and words.

Autotopagnosia from the Greek a and gnosis, meaning "without knowledge", topos meaning "place", and auto meaning "oneself", autotopagnosia virtually translates to the "lack of knowledge about one's own space," and is clinically described as such.

<span class="mw-page-title-main">Integrative agnosia</span> Medical condition

Integrative agnosia is a sub-disease of agnosia, meaning the lack of integrating perceptual wholes within knowledge. Integrative agnosia can be assessed by several experimental tests such as the Efron shape test, which determines the specificity of the disease being Integrative. This disease is often caused by brain trauma, producing medial ventral lesions to the extrastriate cortex. Affecting this region of the brain produces learning impairments: the inability to integrate parts such as spatial distances or producing visual images from short or long-term memory.

Apperceptive agnosia is a failure in recognition that is due to a failure of perception. In contrast, associative agnosia is a type of agnosia where perception occurs but recognition still does not occur. When referring to apperceptive agnosia, visual and object agnosia are most commonly discussed; this occurs because apperceptive agnosia is most likely to present visual impairments. However, in addition to visual apperceptive agnosia there are also cases of apperceptive agnosia in other sensory areas.

Auditory agnosia is a form of agnosia that manifests itself primarily in the inability to recognize or differentiate between sounds. It is not a defect of the ear or "hearing", but rather a neurological inability of the brain to process sound meaning. While auditory agnosia impairs the understanding of sounds, other abilities such as reading, writing, and speaking are not hindered. It is caused by bilateral damage to the anterior superior temporal gyrus, which is part of the auditory pathway responsible for sound recognition, the auditory "what" pathway.

Priming is the idea that exposure to one stimulus may influence a response to a subsequent stimulus, without conscious guidance or intention. The priming effect refers to the positive or negative effect of a rapidly presented stimulus on the processing of a second stimulus that appears shortly after. Generally speaking, the generation of priming effect depends on the existence of some positive or negative relationship between priming and target stimuli. For example, the word nurse might be recognized more quickly following the word doctor than following the word bread. Priming can be perceptual, associative, repetitive, positive, negative, affective, semantic, or conceptual. Priming effects involve word recognition, semantic processing, attention, unconscious processing, and many other issues, and are related to differences in various writing systems. Research, however, has yet to firmly establish the duration of priming effects, yet their onset can be almost instantaneous.

Recognition memory, a subcategory of declarative memory, is the ability to recognize previously encountered events, objects, or people. When the previously experienced event is reexperienced, this environmental content is matched to stored memory representations, eliciting matching signals. As first established by psychology experiments in the 1970s, recognition memory for pictures is quite remarkable: humans can remember thousands of images at high accuracy after seeing each only once and only for a few seconds.

Visual object recognition refers to the ability to identify the objects in view based on visual input. One important signature of visual object recognition is "object invariance", or the ability to identify objects across changes in the detailed context in which objects are viewed, including changes in illumination, object pose, and background context.

Topographical disorientation is the inability to orient oneself in one's surroundings, sometimes as a result of focal brain damage. This disability may result from the inability to make use of selective spatial information or to orient by means of specific cognitive strategies such as the ability to form a mental representation of the environment, also known as a cognitive map. It may be part of a syndrome known as visuospatial dysgnosia.

Form perception is the recognition of visual elements of objects, specifically those to do with shapes, patterns and previously identified important characteristics. An object is perceived by the retina as a two-dimensional image, but the image can vary for the same object in terms of the context with which it is viewed, the apparent size of the object, the angle from which it is viewed, how illuminated it is, as well as where it resides in the field of vision. Despite the fact that each instance of observing an object leads to a unique retinal response pattern, the visual processing in the brain is capable of recognizing these experiences as analogous, allowing invariant object recognition. Visual processing occurs in a hierarchy with the lowest levels recognizing lines and contours, and slightly higher levels performing tasks such as completing boundaries and recognizing contour combinations. The highest levels integrate the perceived information to recognize an entire object. Essentially object recognition is the ability to assign labels to objects in order to categorize and identify them, thus distinguishing one object from another. During visual processing information is not created, but rather reformatted in a way that draws out the most detailed information of the stimulus.

Social-emotional agnosia, also known as emotional agnosia or expressive agnosia, is the inability to perceive facial expressions, body language, and voice intonation. A person with this disorder is unable to non-verbally perceive others' emotions in social situations, limiting normal social interactions. The condition causes a functional blindness to subtle non-verbal social-emotional cues in voice, gesture, and facial expression. People with this form of agnosia have difficulty in determining and identifying the motivational and emotional significance of external social events, and may appear emotionless or agnostic. Symptoms of this agnosia can vary depending on the area of the brain affected. Social-emotional agnosia often occurs in individuals with schizophrenia and autism. It is difficult to distinguish from, and has been found to co-occur with, alexithymia.

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