2D But Not 3D: Pictorial-Depth Deficits in a Case of Visual Agnosia

Abstract

Patients with visual agnosia exhibit acquired impairments in visual object recognition, that may or may not involve deficits in low-level perceptual abilities. Here we report a case (patient DM) who after head injury presented with objectrecognition deficits. He still appears able to extract 2D information from the visual world in a relatively intact manner; but his ability to extract pictorial information about 3D object-structure is greatly compromised. His copying of line drawings is relatively good, and he is accurate and shows apparently normal mental rotation when matching or judging objects tilted in the picture-plane. But he performs poorly on a variety of tasks requiring 3D representations to be derived from 2D stimuli, including: performing mental rotation in depth, rather than in the picture-plane; judging the relative depth of two regions depicted in line-drawings of objects; and deciding whether a line-drawing represents an object that is 'impossible' in 3D. Interestingly, DM failed to show several visual illusions experienced by normals (Muller-Lyer and Ponzo), that some authors have attributed to pictorial depth cues. Taken together, these findings indicate a deficit in achieving 3D intepretations of objects from 2D pictorial cues, that may contribute to object-recognition problems in agnosia.

Trompe l’oeil and the Dorsal/Ventral Account of Picture Perception

“…3 And this is exactly what the findings show. The easier case is the latter: it is welldocumented that visual agnosia patients (that is, patients with lesions in their ventral stream) are incapable of seeing things in pictures (see Turnbull et al 2004 andWestwood et al 2002). D. M., one such patient, can copy the two dimensional lines of a picture but she cannot tell whether these two dimensional lines depict an impossible object.…”

“…D. M., one such patient, can copy the two dimensional lines of a picture but she cannot tell whether these two dimensional lines depict an impossible object. Further, she is not subject to optical illusions (for example, the Müller-Lyer illusion and the Ponzo illusion) that are usually taken to presuppose our ability to see three dimensional objects in two dimensional figures (Turnbull et al 2004). So it seems uncontroversial that the malfunctioning of the ventral stream leads to the malfunctioning of one's abilities to perceive pictures.…”

Differentiating two- from three-dimensional mental rotation training effects

“…Therefore, questions remain concerning the distinction between 2D and 3D mental rotation training effects-that is, what consequences specific training regimens have on mental rotation of different stimuli. This is of particular importance as 2D and 3D mental rotation processes have clearly been distinguished based on distinct neural correlates (Kawamichi, Kikuchi, Noriuchi, Senoo, & Ueno, 2007) and on neuropsychological evidence (Turnbull, Driver, & McCarthy, 2004). Since mental rotation of 2D stimuli and 3D stimuli require different processes, training improvements might not transfer from one type of stimuli to the other.…”

Visual Agnosia for Line Drawings and Silhouettes without Apparent Impairment of Real-Object Recognition: A Case Report

“…In many reported cases of visual agnosia, there is impaired visual recognition of objects, which causes problems in daily life [2,9,16]. Although there is no convincing evidence that our patient's agnosia was restricted to line drawings and silhouettes, as the stimuli of the different tasks (i.e.…”

“…For many patients with visual agnosia, recognition of real objects is superior to recognition of line drawings [3,5,9,16]. Some previous case studies of visual agnosia have shed light on the mechanism of the discrepancy between the recognition of real objects and the recognition of the same objects shown in twodimensional formats.…”