Apperceptive Agnosia: When Seeing Fails

Human visual perception operates as an extraordinarily seamless phenomenon, allowing individuals to effortlessly decipher shapes, contours, and complex scenes into coherent cognitive representations of the physical world. When catastrophic neurological injury disrupts the cortical machinery responsible for structural feature integration, individuals experience apperceptive visual agnosia, a profound neuropsychological condition characterized by the inability to perceive unified visual structures despite preserved elementary visual capacities.

Apperceptive Visual Agnosia

1. Concise Definition

Apperceptive visual agnosia is a neurocognitive visual processing disorder marked by an impairment in synthesizing low-level sensory data—such as luminance, wavelength, and basic orientation—into structured visual percepts. Although individuals retain intact primary sensory pathways, visual acuity, visual fields, and color registration, they cannot reliably discriminate shapes, copy drawings, match identical geometric objects, or recognize visually presented stimuli.

Unlike associative visual agnosia, wherein the structural perceptual representation is preserved while semantic access is severed, apperceptive visual agnosia reflects a failure at the intermediate stages of visual form processing. Patients are essentially unable to formulate a stable “structural description” or perceptual gestalt of an object, leaving them visually stranded in a fragmented sensory environment.

2. Etymology and Linguistic Origin

The linguistic lineage of apperceptive visual agnosia reflects a convergence of nineteenth-century European sensory physiology, structural philosophy, and early neuropsychology. The root term agnosia derives from the Ancient Greek prefix ἀ- (a-, meaning “without” or “lack of”) coupled with γνῶσις (gnōsis, meaning “knowledge” or “recognition”). Sigmund Freud introduced the lexical item “agnosia” into clinical neurology in his 1891 monograph on aphasias (Zur Auffassung der Aphasien) to substitute Heinrich Lissauer’s term “mind-blindness” (Seelenblindheit).

The modifier apperceptive originates from the philosophical and psychological concept of apperception, rooted in the Latin ad- (“toward”) and percipere (“to seize, grasp, or perceive”). Gottfried Wilhelm Leibniz introduced apperception to designate the reflective assimilation of sensory experience into consciousness, a concept later adapted by Immanuel Kant and Wilhelm Wundt. In 1890, German neurologist Heinrich Lissauer operationalized “apperceptive” within clinical neurology to describe the specific breakdown in formulating a unified mental impression of perceived visual sensory inputs, delineating it from the downstream “associative” stage of semantic binding.

3. Pronunciation and Grammatical Form

The term is pronounced phonetically in American English as /æp.ərˈsɛp.tɪv ˈvɪʒ.u.əl æɡˈnoʊ.ʒə/ (or /-zi.ə/) and in British English as /ˌæp.əˈsep.tɪv ˈvɪz.ju.əl æɡˈnəʊ.zi.ə/. Grammatically, the phrase functions as a compound noun phrase within clinical neurology, neuropsychiatry, and cognitive neuroscience. The lexical component apperceptive serves as an classifying adjective derived from the noun apperception, directly qualifying the domain-specific noun visual agnosia.

In formal diagnostic and research contexts, clinicians use the term categorically (e.g., “the patient exhibits classical apperceptive visual agnosia”) or comparatively to denote a spectrum of visual form processing failures (e.g., “an apperceptive pattern of visual deficit”). Inflected and related lexical forms include the noun apperception, the qualifying adjective apperceptual, and the patient descriptor agnosic.

4. Detailed Conceptual Explanation

Apperceptive visual agnosia sits at the critical interface between primary sensation and cognitive recognition. The human visual hierarchy initiates perception when photoreceptors transduce incident light into electrical impulses, which traverse the lateral geniculate nucleus to arrive at the primary visual cortex (striate cortex, or Brodmann area 17/V1). At this early level, basic visual primitives—spatial frequency, oriented line segments, and chromatic contrast—are mapped retinotopically. Under normal conditions, these fragmented local inputs are rapidly organized via intermediate extrastriate visual networks (including areas V2, V3, V4, and lateral occipital areas) through grouping mechanisms, boundary completion, and figure-ground segregation to yield cohesive two- and three-dimensional structural entities.

In patients with apperceptive visual agnosia, the neurobiological machinery governing this intermediate structural integration is profoundly damaged. As a consequence, sensory primitives fail to cohere into a unified perceptual gestalt. When viewing a mundane object, such as a coffee mug, the patient may detect localized horizontal and vertical edges, reflections of light, or the presence of a ceramic surface, but they cannot perceptually resolve these disparate inputs into the continuous form of a vessel with an attached curved handle. Because the perceptual representation itself is degraded, incomplete, or distorted, downstream cognitive modules dedicated to matching the visual percept against stored semantic memory (structural descriptions in long-term memory) cannot be engaged.

A hallmark of apperceptive agnosia is the strict modality-specificity of the recognition deficit. The cognitive architecture responsible for conceptual and semantic knowledge remains completely intact. If the patient is handed the coffee mug or hears the metallic clatter of a spoon inside it, recognition is immediate and unhindered. They can promptly describe its function, name it, and explain its contextual utility. This unimpaired performance across tactile, auditory, and olfactory modalities confirms that the impairment is not an anomic language deficit, global dementia, or generalized intellectual decline, but a selective failure of structural perceptual encoding within the visual modality.

Furthermore, apperceptive agnosia must be differentiated from elementary visual sensory impairments. Patients do not suffer from cortical blindness, visual field loss alone, or absolute scotomata that preclude form detection. Standard ophthalmological evaluations typically reveal preserved visual acuity, normal pupillary light reflexes, intact flicker fusion thresholds, and basic wavelength discrimination. However, the higher-order visual cortex fails to construct the relational topology of visual space, rendering the patient perceptually blind to visual form while simultaneously possessing functional optical apparatuses and intact early sensory registration.

5. Historical Development

The systematic exploration of apperceptive visual agnosia originated in late nineteenth-century European behavioral neurology. In 1890, Heinrich Lissauer published his seminal treatise in the Archiv für Psychiatrie und Nervenkrankheiten, presenting a groundbreaking clinical case of a 80-year-old tradesman who suffered acute recognition failures. Lissauer established a theoretical dichotomy that remains a foundational paradigm in visual neuropsychology: dividing visual object recognition into an initial stage of conscious perceptual construction (Apperzeption) and a subsequent stage of associative semantic linking (Association). Lissauer posited that a defect at the first stage would produce an apperceptive deficit, leaving the individual incapable of discerning or reproducing visual form.

Throughout the early to mid-twentieth century, classical aphasiologists and visual neurologists expanded this concept. Kurt Goldstein and Adhémar Gelb reported on war veterans who had sustained focal occipital shrapnel wounds during World War I, most famously detailing the case of patient Schn., who exhibited profound visual form deficits. Goldstein proposed that such patients lost the innate capacity for “gestalt” perception, relying instead on laborious, conscious compensatory strategies, such as tracing visual contours with head and hand movements to deduce shape identity.

In 1969, D. Frank Benson and Michael Greenberg published a milestone case study that solidified the empirical criteria for pure visual form agnosia. Their patient, Mr. S., had sustained severe anoxic brain injury secondary to accidental carbon monoxide inhalation. Mr. S. demonstrated completely preserved visual acuity, normal color detection, and intact spatial tactile discrimination, yet he could not identify, match, or copy simple letters, numbers, or geometric figures. This case demonstrated beyond doubt that the cortical mechanism for basic shape extraction could be selectively obliterated while sparing elementary visual sensory thresholds.

In the 1980s and 1990s, British cognitive neuropsychologist Elizabeth Warrington and her collaborators introduced critical psychometric refinements to Lissauer’s dichotomy. Warrington argued that apperceptive visual agnosia was not a monolithic impairment, demonstrating that perceptual processing unfolds across multiple discrete stages: from basic shape detection, through perceptual categorization (the ability to recognize an object across atypical orientations and lighting conditions), to semantic access. Concurrently, cognitive scientists David Marr and later Irvin Biederman integrated computational modeling into visual agnosia, providing algorithmic frameworks for understanding the specific computational stages that collapse during apperceptive failure.

6. Theoretical Foundations

The theoretical architecture of apperceptive visual agnosia is intrinsically bound to contemporary computational and cognitive theories of vision. The most influential foundation remains David Marr‘s computational theory of visual processing. Marr conceptualized human vision as a sequential progression through three representational tiers:

• The Primal Sketch: Encodes zero-crossings, luminance gradients, edges, orientations, and blobs from the two-dimensional retinal array.
• The 2.5D Sketch: Synthesizes depth cues, surface orientation, texture gradients, and local contours into a viewer-centered representation of visible surfaces.
• The 3D Model: Transforms viewer-centered sketches into volumetric, object-centered representations composed of generalized cones and structural primitives that remain invariant despite changes in vantage point.

Within Marr’s framework, classical apperceptive visual agnosia corresponds directly to a profound catastrophic breakdown occurring during the construction of the primal sketch into the 2.5D sketch. The patient cannot compute the spatial relationships among local surface features, preventing the realization of a coherent structural percept. In less severe forms, such as perceptual categorization deficits, early primal sketch synthesis remains functional, but the patient fails to derive an object-centered 3D model, leaving them vulnerable to perspective distortions.

Another primary theoretical pillar is the dual-stream hypothesis formulated by Melvyn Goodale and A. David Milner in 1992. Building on earlier non-human primate work by Ungerleider and Mishkin, Goodale and Milner proposed that visual cortical processing bifurcates into two anatomically and functionally distinct processing streams:

• The Ventral Stream: Projecting from the primary visual cortex (V1) to the inferior temporal lobe, mediating perception-for-recognition (the “what” pathway).
• The Dorsal Stream: Projecting from V1 to the posterior parietal cortex, mediating online spatial visuomotor action (the “how” or “where” pathway).

Goodale and Milner tested this dissociation extensively through their celebrated patient, D.F., who acquired permanent visual form agnosia following bilateral ventral occipital damage from carbon monoxide poisoning. While D.F. was entirely incapable of identifying, copying, or visually discriminating the orientation of a simple slot (e.g., whether it was horizontal, vertical, or tilted at 45 degrees), she exhibited flawless manual motor execution when tasked with posting a handheld card into that exact same slot. Her visual motor system effortlessly computed the spatial orientation of the target in real time via the intact dorsal stream, despite the profound collapse of her ventral-stream conscious visual perception. This dissociation placed apperceptive visual agnosia firmly within the computational domain of the ventral visual processing stream.

7. Key Components, Types, and Dimensions

Contemporary cognitive neuropsychology recognizes that apperceptive visual agnosia is not an indivisible entity, but rather a spectrum of visual structural breakdowns corresponding to distinct anatomical and computational loci along the visual processing hierarchy:

• Visual Form Agnosia: The most severe and prototypical manifestation. Patients exhibit an inability to perceive the most elementary properties of shape, contour, and orientation. They cannot discriminate between a circle and a square, copy line drawings, or visually match identical geometric shapes, despite retaining normal visual acuity, color discrimination, and motion detection. It typically results from bilateral ventrolateral occipital lesions caused by anoxia or carbon monoxide poisoning.
• Apperceptive Morphological Agnosia (Shape Agnosia): Characterized by the preservation of very basic edge detection, but a breakdown in boundary completion, contour integration, and figure-ground segmentation. Patients can detect individual lines and orientation bars, but fail completely when required to integrate those lines into bounded shapes or distinguish overlapping silhouettes.
• Integrative Agnosia: A subtype formally delineated by Riddoch and Humphreys (1987) via patient H.J.A. Patients retain the ability to perceive individual visual features, identify elementary geometric forms, and even laboriously copy simple objects line by line. However, they fail to integrate these localized components into a cohesive structural gestalt. When presented with complex, multi-part objects, they perceive an unintegrated collection of constituent parts, misinterpreting the overall object by anchoring their judgment to an isolated component.
• Transformational / Perceptual Categorization Deficit: A higher-level apperceptive variant identified by Elizabeth Warrington. Patients perceive prototypical, canonical views of objects without difficulty and can copy standard representations accurately. However, their recognition fails dramatically when stimuli are presented from unusual viewpoints (e.g., a bucket viewed directly from above), under extreme foreshortening, or under casting shadows. The impairment reflects an inability to achieve object constancy across transformations in coordinate space.
• Dorsal Simultanagnosia: Often categorized in conjunction with Balint syndrome, this form represents a spatial perceptual breakdown wherein patients can perceive only a single visual object or localized detail at any given moment, remaining functionally blind to all surrounding stimuli. It arises from bilateral parieto-occipital damage and disrupts the broad simultaneous apprehension of scenes.

8. Examples and Illustrative Cases

The behavioral manifestations of apperceptive visual agnosia present striking clinical phenomena. In clinical examinations, a patient presented with an ordinary safety pin may stare at it blankly. When queried about what they see, they may note “a glint of shine” or “a silver line,” unable to register the closed loop or the point of the clasp. If the clinician drops the safety pin onto a table, producing its characteristic metallic sound, or places it in the patient’s hand, the patient immediately identifies it: “Oh, that is an open safety pin, be careful not to poke yourself.”

In a famous historical case investigated by Goodale and Milner, patient D.F. was asked to draw a simple apple placed directly before her. Because her ventral processing stream could not formulate the perceptual representation of the fruit’s circular boundary and stem, her copied drawing consisted of random, disjointed lines that bore no resemblance to an apple. Yet, when asked moments later to draw an apple “from memory,” she utilized preserved internal conceptual representations stored in semantic and motor memory to execute a recognizable outline of an apple with a stem. When subsequently presented with her own freshly executed drawing, she was entirely unable to identify what she had just drawn.

Another illustrative case is patient H.J.A., studied by Jane Riddoch and Glyn Humphreys. H.J.A. could perceive basic contours and was capable of drawing intricate copies of complex stimuli, such as a paintbrush or an owl, through an agonizingly slow, point-to-point drafting technique. However, because he could not rapidly integrate these lines into a unified visual perceptual unit, he had no comprehension of what he was drawing while producing it. When shown a drawing of an inverted carrot, he identified it as a “paintbrush with unruly bristles,” having fixated upon the leafy greens and failed to integrate them with the tapered root body.

9. Measurement and Assessment

The clinical assessment of apperceptive visual agnosia requires a rigorous, hierarchical psychometric methodology designed to systematically isolate sensory, perceptual, and semantic processing tiers:

• Exclusion of Primary Visual Sensory Loss: Comprehensive neuro-ophthalmological screening must establish that the impairment cannot be accounted for by visual acuity deficits, severe scotomata, optical aberrations, or visual field neglect. Perimetry, Snellen chart testing, and contrast sensitivity assessments are performed.
• Efron Shape Discrimination Test: Introduced by Robert Efron, this foundational test presents pairs of geometric stimuli consisting of squares and rectangles matched precisely for total surface area and luminance. The subject must indicate whether two presented stimuli are identical or different based solely on aspect ratio. Failure on the Efron test indicates visual form agnosia.
• Visual Copying and Matching Tasks: Patients are instructed to copy basic geometric figures (circles, crosses, triangles) and complex figures (such as the Rey-Osterrieth Complex Figure). Patients with pure apperceptive visual agnosia fail drastically at copying, producing formless, disorganized lines. Similarly, matching-to-sample tasks using identical or rotated two-dimensional shapes reveal an inability to establish shape equivalence.
• Overlapping Figures and Figure-Ground Tests: The Poppelreuter-Ghent Overlapping Figures Test presents line drawings of multiple familiar objects superimposed on top of one another. Patients with apperceptive or integrative agnosia cannot segregate intersecting boundaries, leading to an inability to parse individual objects from the visual noise.
• Birmingham Object Recognition Battery (BORB): Developed by Humphreys and Riddoch, the BORB is a standardized neuropsychological instrument specifically calibrated to evaluate visual processing stages. Subtests evaluate minimal feature match, shape discrimination, length and orientation judgment, overlapping figure detection, and object decision (distinguishing real objects from chimera non-objects).
• Unusual Views and Foreshortened Views Tests: Warrington’s Unusual Views Test presents real-world objects photographed from both canonical (standard) and non-canonical (atypical) vantage points. Patients with higher-order perceptual categorization deficits succeed on canonical presentations but fail catastrophically when perspective foreshortening disrupts standard two-dimensional profiles.

10. Applications and Practical Significance

Understanding apperceptive visual agnosia carries vital practical implications across neurological medicine, rehabilitation therapy, assistive engineering, and computational modeling. In acute clinical practice, the recognition of an apperceptive deficit serves as an imperative diagnostic indicator of diffuse or bilateral ventral occipital and temporal cortical insult. It frequently alerts clinical teams to the neurological sequelae of profound cerebral hypoxia, sustained cardiac arrest, carbon monoxide poisoning, severe basilar artery stroke, or atypical neurodegenerative presentations such as posterior cortical atrophy (the visual variant of Alzheimer’s disease).

In cognitive rehabilitation, classical restorative interventions designed to “re-train” visual form perception frequently yield minimal functional recovery due to the permanent destruction of intermediate cortical networks. Consequently, clinical neuropsychologists and occupational therapists formulate compensatory paradigms. Patients are taught to bypass damaged ventral streams by leveraging preserved dorsal-stream visuomotor tracking, kinesthetic exploration, and multimodal sensory integration. For example, patients learn to consciously scan for distinct surface textures, identify unique acoustic signatures of objects, or actively manipulate physical items with their hands to induce haptic object identification.

Furthermore, apperceptive visual agnosia offers foundational insights for computer vision and artificial intelligence architectures. Early computer vision systems frequently mimicked an extreme form of apperceptive agnosia, struggling to recognize objects when partial occlusions, unconventional rotations, or dynamic lighting conditions were introduced. By analyzing the algorithmic stages where human visual synthesis breaks down, neural network researchers have refined deep convolutional neural networks (CNNs) and transformer models to incorporate robust intermediate feature integration and invariant structural descriptions, mirroring biological vision.

11. Research and Empirical Evidence

Decades of neuroimaging and electrophysiological research have expanded our understanding of the structural and functional substrates underlying apperceptive visual agnosia. Early post-mortem neuropathology consistently localized the structural lesions of visual form agnosia to bilateral infarction or necrosis of the lateral and ventral occipital cortices, often extending into the adjacent posterior fusiform and lingual gyri, typically sparing the primary striate cortex (V1) but devastating visual areas V2, V3, and lateral occipital complex (LOC).

Modern neuroimaging studies utilizing functional magnetic resonance imaging (fMRI) have systematically confirmed the pivotal role of the lateral occipital complex. In neurotypical individuals, the LOC responds selectively to structured geometric shapes and coherent objects compared to scrambled visual arrays matched for luminance and spatial frequency. Functional imaging investigations conducted on brain-damaged agnosic individuals, notably re-examinations of patient D.F. by James, Culham, Humphrey, Milner, and Goodale (2003), demonstrated that her LOC exhibited completely flat activation profiles when exposed to structural forms, mirroring its anatomical destruction. Despite this failure in the ventral stream, functional activation within her dorsal parietal networks remained intact during visuomotor grasping tasks, validating the functional separation of vision-for-perception and vision-for-action.

Event-related potential (ERP) studies have similarly charted the temporal dynamics of apperceptive breakdown. Early sensory visual evoked potentials, such as the C1 (originating in striate cortex within 50–90 ms) and the P1 (peaking around 100 ms in extrastriate cortex), remain largely preserved in apperceptive patients. However, downstream perceptual closure waveforms—specifically the N1 component (150–200 ms) and the subsequent visual structural N250—are absent or grossly disorganized. These electrophysiological markers provide direct empirical verification that basic sensory signals enter the visual cortex intact, but intermediate temporal binding and structural categorization fail prior to the activation of semantic networks around 400 ms (N400).

12. Cultural and Cross-Cultural Considerations

Because apperceptive visual agnosia represents a fundamental neurobiological breakdown of basic perceptual synthesis, its core physiological features manifest consistently across all human populations. However, the operationalization, diagnosis, and socio-functional impact of the condition are mediated by cultural, linguistic, and educational variables. Standardized diagnostic batteries, such as the Birmingham Object Recognition Battery or the Boston Naming Test, rely heavily on two-dimensional line drawings and cultural artifacts (e.g., specific utensils, tools, or architectural features) that assume familiarity with particular socio-cultural environments.

Cross-cultural cognitive research demonstrates that individuals from cultures with low formal literacy or minimal exposure to pictorial representations (such as Western-style linear perspective) process two-dimensional structural line drawings differently than individuals with extensive visual media literacy. An uneducated individual tested with stylized Western line drawings might struggle with perspective interpretation, potentially resulting in misdiagnoses of integrative or transformational agnosia if clinicians do not utilize culturally adapted, ecologically valid stimuli. Neuropsychologists operating in diverse global contexts must utilize three-dimensional real-world objects and culturally universal forms to prevent confounding cultural familiarity with neurological apperceptive dysfunction.

13. Criticisms, Debates, and Limitations

Despite its enduring presence in neuropsychological taxonomy, the classification of apperceptive visual agnosia has sparked substantial theoretical controversy. The primary debate centers on whether a pure apperceptive agnosia can truly exist in complete isolation from subtle low-level sensory impairments. Early skeptics, such as Bay (1953) and Bender and Feldman (1972), argued that patients diagnosed with apperceptive agnosia simply suffered from complex combinations of elementary sensory deficits—such as constricted visual fields, impaired contrast sensitivity, abnormal local dark adaptation, and rapid sensory fatigue—which together degraded visual input to a degree that prevented form recognition.

While the meticulous study of cases like patient Mr. S. (Benson & Greenberg, 1969) and patient D.F. (Milner et al., 1991) largely refuted the extreme view that all agnosia is sensory failure, debate continues regarding the boundaries of the construct. Many cognitive scientists criticize Lissauer’s original dichotomy as overly simplistic, arguing that dividing visual recognition into a binary “apperceptive versus associative” division fails to capture the continuous, interactive nature of visual cognition. Visual processing is not an entirely bottom-up, unidirectional pipeline; extensive top-down feedback loops continuously descend from frontal and temporal semantic areas into early extrastriate cortices to guide perceptual hypothesis testing and figure-ground resolution.

Another continuous debate focuses on the distinction between apperceptive agnosia and simultanagnosia. Some theorists argue that dorsal simultanagnosia is fundamentally a disorder of spatial attention rather than a disorder of form perception per se, questioning its placement under the broader heading of apperceptive agnosia. Similarly, researchers dispute whether integrative agnosia constitutes a distinct intermediate stage or merely reflects an incomplete, mild manifestation of visual form agnosia.

14. Related Terms and Distinctions

To avoid diagnostic confusion, apperceptive visual agnosia must be clearly distinguished from several related neuropsychological syndromes:

• Associative Visual Agnosia: In associative agnosia, perceptual structural synthesis is intact. The patient can accurately copy complex line drawings, match identical shapes, and group objects by physical appearance. However, they cannot link this preserved structural representation to semantic memory; they do not know what the object is or what purpose it serves unless accessed through another modality.
• Optic Aphasia: A selective visual-verbal disconnection syndrome. The patient perceives the object normally (they can copy it and draw it) and comprehends its meaning (they can pantomime its correct functional use with their hands), but they cannot retrieve its spoken lexical name purely from visual presentation.
• Visual Anomia: A language-based naming deficit wherein the patient cannot name objects across any modality, visual or otherwise, though their perceptual synthesis and conceptual comprehension remain intact.
• Cortical Blindness: A profound loss of conscious vision resulting from extensive bilateral destruction of the primary visual cortex (V1). Patients have lost elementary visual sensations (acuity, light perception), unlike apperceptive agnosics whose striate cortex and low-level sensory thresholds remain substantially functional.
• Visual Form Agnosia: Frequently used interchangeably with classical apperceptive agnosia, this specific term denotes the severe inability to extract basic geometric contours and shapes, representing the most extreme manifestation of the apperceptive spectrum.
• Prosopagnosia: A modality-specific visual agnosia characterized by the inability to recognize familiar human faces. While it can possess an apperceptive subtype (inability to perceive facial structure or configuration), it is generally distinguished by its category-specificity for facial architecture, leaving non-face object recognition relatively preserved.

15. Summary and Key Takeaways

Apperceptive visual agnosia represents one of the most profound and clarifying neurological disruptions of human consciousness. It is characterized by the selective breakdown of intermediate visual processing, wherein the brain loses the capacity to synthesize low-level sensory features into coherent, structured visual shapes, contours, and objects. The condition manifests despite preserved primary visual acuity, color discrimination, and elementary sensory transduction, and remains strictly limited to the visual modality, leaving semantic cognition, intellectual functioning, and tactile/auditory recognition entirely intact.

Arising predominantly from bilateral ventral occipital and extrastriate damage following cerebral anoxia, stroke, or toxic exposure, apperceptive visual agnosia illuminates the complex functional architecture of the human brain. It provides empirical confirmation of the modular separation between low-level sensation, ventral-stream structural perception, dorsal-stream visuomotor action, and semantic association. The condition underscores that human sight is not a passive reception of external imagery, but an active, complex neurocomputational construction of structural reality.

References

• Benson, D. F., & Greenberg, J. P. (1969). Visual form agnosia: A specific defect in visual knowledge. Archives of Neurology, 20(1), 82–89. https://doi.org/10.1001/archneur.1969.00480070092010
• Efron, R. (1968). What is perception? Boston Studies in the Philosophy of Science, 4, 137–173. https://doi.org/10.1007/978-94-010-3381-7_4
• Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways for perception and action. Trends in Neurosciences, 15(1), 20–25. https://doi.org/10.1016/0166-2236(92)90344-8
• Humphreys, G. W., & Riddoch, M. J. (1987). To see but not to see: A case study of visual agnosia. Lawrence Erlbaum Associates.
• James, T. W., Culham, J., Humphrey, G. K., Milner, A. D., & Goodale, M. A. (2003). Ventral occipital lesions impair object recognition but not object-directed grasping: An fMRI study. Brain, 126(11), 2463–2475. https://doi.org/10.1093/brain/awg248
• Lissauer, H. (1890). Ein Fall von Seelenblindheit nebst einem Beitrage zur Theorie derselben. Archiv für Psychiatrie und Nervenkrankheiten, 21(2), 222–270. https://doi.org/10.1007/BF02226765
• Marr, D. (1982). Vision: A computational investigation into the human representation and processing of visual information. W. H. Freeman.
• Milner, A. D., Perrett, D. I., Johnston, R. S., Benson, P. J., Jordan, T. R., Heeley, D. W., Bettucci, D., Mortara, F., Mutani, R., Terazzi, E., & Davidson, D. L. (1991). Perception and action in visual form agnosia. Brain, 114(1), 405–428. https://doi.org/10.1093/brain/114.1.405
• Warrington, E. K. (1985). Agnosia: The impairment of object recognition. In P. J. Vinken, G. W. Bruyn, & H. L. Klawans (Eds.), Handbook of Clinical Neurology (Vol. 45, pp. 333–349). Elsevier Science Publishers.