Pseudoneglect for mental alphabet lines is affected by prismatic adaptation

Abstract

While patients with right parietal damage and spatial neglect bisect lines to the right, the general population bisects lines to the left; a phenomenon known as pseudoneglect. The leftward bias also occurs for mental representations, such as number and alphabet lines. Prismatic adaptation can have a dramatic effect on attentional bias and corrects neglect and pseudoneglect for physical and mental number lines. This study examined whether prismatic adaptation can correct leftward bisection biases for alphabet lines, which may have a different spatial arrangement compared to number lines. In pre-adaptation testing, students (n = 42) were shown letter trigrams (e.g. C H P) and judged whether the alphabetical distance before or after the inner-letter was larger. Participants were then split into three groups and were adapted to left-shifting, control or right-shifting prims. After adaptation, the mental alphabet bisection task was re-administered. The length of left side of the alphabet lines was overestimated by all three groups in the pre-adaptation phase. Right-shifting prisms and control spectacles had no effect on the leftward bias whereas exposure to left-shifting prisms corrected the bias. The results replicate an effect observed for mental number lines and demonstrate that low-level sensory-motor shifts can correct attentional biases associated with high-level representations, such as letters.