Is This Within Reach? Left but Not Right Brain Damage Affects Affordance Judgment Tendencies

Abstract

The ability to judge accurately whether or not an action can be accomplished successfully is critical for selecting appropriate response options that enable adaptive behaviors. Such affordance judgments are thought to rely on the perceived fit between environmental properties and knowledge of one's current physical capabilities. Little, however, is currently known about the ability of individuals to judge their own affordances following a stroke, or about the underlying neural mechanisms involved. To address these issues, we employed a signal detection approach to investigate the impact of left or right hemisphere injuries on judgments of whether a visual object was located within reach while remaining still (i.e., reachability). Regarding perceptual sensitivity and accuracy in judging reachability, there were no significant group differences between healthy controls (N = 29), right brain damaged (RBD, N = 17) and left brain damaged stroke patients (LBD, N = 17). However, while healthy controls and RBD patients demonstrated a negative response criterion and thus overestimated their reach capability, LBD patients' average response criterion converged to zero, indicating no judgment tendency. Critically, the LBD group's judgment tendency pattern is consistent with previous findings in this same sample on an affordance judgment task that required estimating whether the hand can fit through apertures (Randerath et al., 2018). Lesion analysis suggests that this loss of judgment tendency may be associated with damage to the left insula, the left parietal and middle temporal lobe. Based on these results, we propose that damage to the left ventro-dorsal stream disrupts the retrieval and processing of a stable criterion, leading to stronger reliance on intact on-line body-perceptive processes computed within the preserved bilateral dorsal network.

Keywords: affordances; decision making; lesion analysis; perception action; reachability; stroke.

Figure 1

The figure depicts the measurement procedure (A), the Reachability Task (B) and the control task including perceptual estimations (C). Participants were seated centrally in front of the reaching apparatus. The example shows a setting for the right hand (RBD and CR group). (A) To determine the maximum reach participants successively pushed the object as far as possible with their index-finger along each of the three tracks, while goggles were closed. Bending forward was allowed but the bottom needed to stay seated. (B) Upon vision, participants were asked to respond as accurate as possible whether they judged the object to be reachable, by pressing a designated yes or no button. (C) The participants said stop, when they decided that the moving object was aligned with the object next to the track and were allowed to indicate final adjustments. The image depicts a trial in which the object was moved toward the participant.

Figure 2

Hit and False-Alarm rates for LBD patients, RBD patients and age-matched healthy controls. The figure displays an overview of changes in Hit- and False-Alarm rates for the different distances across tracks. The value “0” reflects a trial with an object presented at the individually-defined maximum reachable distance. Distance-values represent deviations (cm) from the individual's maximum reachable target. Objects presented at positions with negative distance-values were located within the participant's actual reach (correct response: yes), and those with positive distance-values were located out of reach (correct response: no). The graphs display a typical distribution with higher Hit and lower False-Alarm rates for distances that are considerable further away from the physical constraints. Conversely, judgment performance for distances closer to the maximum reach (0) decreased.

Figure 3

Judgment tendencies in RBD patients in relation to scores of self-estimated motor abilities (0: no problem to 3: problem). The worse RBD patients estimated their own bodily capabilities the more their criterion deviated from typical tendencies made by healthy subjects in the reachability task, converging to a 0-criterion.

Figure 4

Overlays of LBD patients' (A) and RBD patients' (B) lesion maps. The color bar indicates degree of overlap of lesions out of 17 patients. MNI coordinates of each transverse section are given.

Figure 5

VLSM for the Reachability Task as well as subtraction analyses of the criterion in the Reachability Task. Statistical maps (upper graph) display voxels corresponding to a criterion close to zero, thereby stressing lesion sites of patients that had chosen no judgment tendency in the Reachability Task. Please note that in NPM analysis, only voxels were considered that were damaged in more than 10% of patients. Subtraction plots (lower graph) display voxels corresponding to a criterion close to zero, thereby stressing lesion sites of patients that had chosen no judgment tendency compared to patients that demonstrated a specific judgment tendency in the Reachability Task. Regions that were associated with a deviation from typical judgment tendencies were mainly located within the left insular, the left inferior parietal and the left middle superior temporal lobe. MNI coordinates of each transverse section are given.

Figure 6

Working model providing first indications for essential regions for perceptual sensitivity and judgment tendencies in affordance judgments. In the light of the discussed results, we here propose a working model for essential elements when performing affordance judgments. For illustration purposes only, we here used the visually more clearly depicted VLSM results. In our working model, essential regions for judgment tendencies are depicted in orange (based on the Reachability Task, Figure 5) and those for perceptual sensitivity are displayed in green [based on the Aperture Task, (Randerath et al., 2018)]. The left hemisphere dominance for judgment tendency is highlighted.