Neglect disrupts the mental number line

Abstract

A popular metaphor for the representation of numbers in the brain is the 'mental number line', in which numbers are represented in a continuous, quantity-based analogical format. Here we show that patients with hemispatial neglect misplace the midpoint of a numerical interval when asked to bisect it (for example, stating that five is halfway between two and six), with an error pattern that closely resembles the bisection of physical lines. This new form of representational neglect constitutes strong evidence that the mental number line is more than simply a metaphor, and that its spatial nature renders it functionally isomorphic to physical lines.

Biased numerical cognition impairs economic decision‐making in Parkinson's disease

“…Participants were required to estimate the midpoint (within 6 sec to avoid calculation) of the two numerical magnitudes across the following 20 trials presented in the following temporal sequence (randomized order) (33‐87), (32‐89), (37‐91), (93‐39), (66‐41), (68‐44), (47‐90), (48‐92), (52‐91),(92‐56), (89‐57), (87‐59), (61‐99), (63‐97), (67‐95) (99‐67), (58‐124), (131‐59), (131‐55), and (58‐132) 5, 10, 18. Note, as evident from the trials above, the number presented on the left of the pair varied from being either the larger or the smaller value, to avoid any effects associated with either spatial or temporal biasing.…”

“…Bisection errors were calculated by subtracting the arithmetical midpoint from the participant‐reported midpoint which we converted into percentage bisection errors by dividing the errors with the number interval size. Positive mean % bisection errors denote an overestimation, whereas negative mean % bisection errors denote underestimation from the actual midpoint 5, 10, 18…”

“…Previous neuropsychological studies have demonstrated that right hemisphere fronto‐parietal lesions that invoke a rightward spatial attentional bias can induce an isomorphic pathological bias toward larger magnitudes 5. Critically, subsequent research has illustrated that such pathological biases in numerical magnitude allocation are dissociated from any spatial attention bias 6, 8…”

“…In healthy individuals, we have recently illustrated the critical role of mechanisms associated with numerical magnitude allocation upon economic choice selection during decision‐making (Arshad et al., In‐press). Given that neurological dysfunction can impair magnitude perception,5, 6 herewith we ask whether (1) Parkinsonian patients exhibit biases in numerical magnitude allocation and (2) whether these biases can functionally impair decision‐making.…”

“…Currently, however, the precise neural mechanisms that underpin numerical magnitude allocation remain unclear 5, 6, 7, 8, 9, 10. Previous neuropsychological studies have demonstrated that right hemisphere fronto‐parietal lesions that invoke a rightward spatial attentional bias can induce an isomorphic pathological bias toward larger magnitudes 5.…”