Real-world size coding of solid objects, but not 2-D or 3-D images, in visual agnosia patients with bilateral ventral lesions

Abstract

Patients with visual agnosia show severe deficits in recognizing two-dimensional (2-D) images of objects, despite the fact that early visual processes such as figure-ground segmentation, and stereopsis, are largely intact. Strikingly, however, these patients can nevertheless show a preservation in their ability to recognize real-world objects -a phenomenon known as the 'real-object advantage' (ROA) in agnosia. To uncover the mechanisms that support the ROA, patients were asked to identify objects whose size was congruent or incongruent with typical real-world size, presented in different display formats (real objects, 2-D and 3-D images). While recognition of images was extremely poor, real object recognition was surprisingly preserved, but only when physical size matched real-world size. Analogous display format and size manipulations did not influence the recognition of common geometric shapes that lacked real-world size associations. These neuropsychological data provide evidence for a surprising preservation of size-coding of real-world-sized tangible objects in patients for whom ventral contributions to image processing are severely disrupted. We propose that object size information is largely mediated by dorsal visual cortex and that this information, together with detailed representation of object shape which is also subserved by dorsal cortex, serve as the basis of the ROA.

Keywords: Object recognition; Real-world objects; Real-world size; Two-dimensional images; Visual form agnosia.

Figure 1:. Anatomical scans for patients D.F. and J.W.

High resolution MRI scan of D.F.’s brain (upper panel) and a computed tomography (CT) scan of J.W.’s brain (lower panel). Axial slices are displayed in ascending order from left (ventral) to right (dorsal).

Figure 2:. Stimuli used in Experiments 1–3.

(A) Stimuli in Experiment 1: Half were exemplars whose physical size (Φ) was congruent (C) with typical real-world size (RWS); the remainder were ‘miniaturized’ items whose size was incongruent small (I_S) with real-world size. (B) Stimuli in Experiment 2: 3-D-printed objects whose size was scaled to be smaller than (50%, I_S), congruent with (100%, C), or larger than (150%, I_L), typical real-world size. (C) Stimuli in Experiment 3: Common geometric shapes without strong real-world size associations.

Figure 3:. Recognition of Size-Congruent (C) vs. Size-Incongruent (I_S) Real Objects and Images

(A) The patients (D.F., upper panel; J.W., lower panel) named objects presented in different Display Formats (real objects, 3-D images, 2-D images). Stimuli were presented in different Viewing Conditions: with or without depth cues from motion parallax (head position free vs. fixed in chin rest) and binocularly disparity (binocular vs. monocular vision). (B) % correct responses, shown separately for stimuli in each Display Format, Size (C, I_S) and Viewing Condition. (C) Facilitatory effect of size-congruence for stimuli in each Display Format and Viewing Condition. (D) Error analysis: % trials where target was misidentified as another ‘small’ or ‘large’ object (or no response), separately for each Display Format and Viewing Condition. Data averaged across conditions shown far right (black bars).

Figure 4. Recognition of Size-Congruent (C) vs. Size-Incongruent Small (I_S) and Large (I_L) Objects

(A) % correct responses by D.F. (upper panel) and J.W. (lower panel) for real objects and 2-D images, separately for stimuli in each Size condition. All stimuli viewed binocularly with fixed head position. (B) Facilitatory effect of size-congruence for real objects vs. 2-D images. (C) % trials where target was misidentified as a ‘small’ or ‘large’ object (or no response) separately for stimuli in each Display Format. Data averaged across Display Formats shown far right (black bars).

Figure 5:. Recognition of Geometric Shapes

% correct responses made by D.F. (left panel) and J.W. (right panel) in naming geometric shapes displayed as real objects or 2-D images, separately for small (S), medium (M), and large (L) sizes.