The centre is not in the middle: spatial biases in the bisection of different visual stimuli

There is evidence that the spatial extent of written words is misperceived in normal reading. The left bias frequently founded in the bisection of orthographic material has been interpreted as resulting from an attentional bias towards the beginning of the word and the lexical or visuo-spatial nature (pseudoneglect) of this bias is still debated. Besides eye movements studies reported an opposite asymmetry in visual exploration of continuous (lines) and discrete (ortographical) material in left and right emispace. In order to investigate to what extent lexical access is responsible for this distortion and the impact of visuo-perceptual factors (i.e. length) on different material (stimulus continuity), five experiments required Italian readers to identify the centre of lines, words, pseudowords, consonant strings and graphic strings. The stimulus length was confirmed as a critical factor in the bisection performance across the five experiments that showed a left bias for lines, while discrete strings induced a left bias only when they were long and a right error if short. Moreover, essentially in discrete strings length proportionally modulates bias size. Overall, these findings suggest that different visuo-perceptual effects on bisection of continuous and discrete material reflect a different visual exploration that they require.