Revisiting the Landmark Task as a tool for studying hemispheric specialization: What's really right?

Abstract

The "Landmark Task" (LT) is a line bisection judgment task that predominantly activates right parietal cortex. The typical version requires observers to judge bisections for horizontal lines that cross their egocentric midline and therefore may depend on spatial attention as well as spatial representation of the line segments. To ask whether the LT is indeed right-lateralized regardless of spatial attention (for which the right hemisphere is known to be important), we examined LT activation in 26 neurologically healthy young adults using vertical (instead of horizontal) stimuli, as compared with a luminance control task that made similar demands on spatial attention. We also varied task difficulty, which is known to affect lateralization in both spatial and language tasks. Despite these changes to the task, we observed right-lateralized parietal activations similar to those reported in other LT studies, both at group level and in individual lateralization indices. We conclude that LT activation is robustly right-lateralized, perhaps uniquely so among commonly-studied spatial tasks. We speculate that the unique properties of the LT reside in its requirement to judge relative magnitudes of the two line segments, rather than in the more general aspects of spatial attention or visual-spatial representation.

The Allocation of Vertical Attention in Patients with End-Stage Renal Disease Receiving Dialysis

“…Seydell-Greenwald and colleagues (2019) examined neurologically healthy young adults using the landmark test with vertical instead of horizontal stimuli. These investigators found right-lateralized parietal activations similar to those reported in other landmark tests with horizontal lines [18].…”

Development of bilateral parietal activation for complex visual‐spatial function: Evidence from a visual‐spatial construction task

“…Importantly, we do not intend to suggest that all visual‐spatial functions start out with a bilateral pattern of activation early in life and remain this way throughout development. Indeed, studies assessing the lateralization of other spatial tasks in adults, such as line bisection, suggest that the right hemisphere plays a predominant role, with little involvement of the left (Cavézian et al, 2012; Çiçek et al, 2009; Fink et al, 2000; Seydell‐Greenwald et al, 2019). It is notable, however, that the “puzzle game” used in the present study is based on the block construction task, which is one of the most widely used instruments to evaluate spatial abilities.…”

Developmental changes in neural lateralization for visual‐spatial function: Evidence from a line‐bisection task

“…Third, as reviewed by Seydell‐Greenwald et al. (2019), using a vertical line presented at screen center minimizes activations associated with shifts in spatial attention to left or right hemispace, which could influence lateralization of activation patterns (Corbetta et al., 1993; Corbetta & Shulman, 2011; Heilman & van den Abell, 1980; Mesulam, 1981). Thus, we are able to isolate right‐lateralized activation associated with the spatial computations involved in comparison of relative length and proportion, without also drawing in activation that may be associated with left/right shifts in attention.…”

“…First, as reviewed above, it has been shown that this task elicits robust right‐lateralized parietal activation, regardless of whether the stimulus lines are presented in vertical or horizontal orientations (Fink et al., 2001). Second, we aimed to build upon the findings of a previous study of adults (Seydell‐Greenwald et al., 2019), which also used vertical lines. Third, as reviewed by Seydell‐Greenwald et al.…”

“…1 As a check to ensure that different levels of smoothing did not impact our results, data were also analyzed using an 8 mm FWHM Gaussian kernel (which is the level of spatial smoothing used to analyze adult data in Seydell-Greenwald et al, 2019). Findings were comparable and not qualitatively different for 3 mm and 8 mm smoothing.…”