Spatial biases in peripersonal space in sighted and blind individuals revealed by a haptic line bisection paradigm.

Abstract

Our representation of peripersonal space does not always accurately reflect the physical world. An example of this is pseudoneglect, a phenomenon in which neurologically normal individuals bisect to the left of the veridical midpoint, reflecting an overrepresentation of the left portion of space compared with the right one. Consistent biases have also been observed in the vertical and radial planes. It is an open question whether these biases depend on normal visual experience for their occurrence. Here we systematically investigated this issue by testing blindfolded sighted and early blind individuals in a haptic line bisection task. Critically, we found a robust leftward bias in all participants. In the vertical and radial planes, sighted participants showed a consistent downward and proximal bias. Conversely, the directional bias in blind participants was dependent on the final movement direction; thus, there was no general bias in either direction. These findings are discussed in terms of different reference frames adopted by sighted and blind participants when encoding space.

Native Reading Direction and Corresponding Preferences for Left- or Right-Lit Images

“…Leftward biases also occur in lighting of artwork (Sun & Perona, 1998) and in advertisements (Thomas, Burkitt, Patrick, & Elias, 2008) and advertisement lighting preferences (Hutchison, Thomas, & Elias, 2011). In line bisection, humans make leftward bisection errors in pen-and-paper tasks (MacDonald-Nethercott, Kinnear, & Venneri, 2000;McCourt, 2001) as well as in haptic bisection tasks (Cattaneo, Fantino, Tinti, Pascual-Leone, Silvanto, & Vecchi, 2011), while young chickens (Gallus gallus domesticus) also make leftward errors while pecking at lines of beads (Regolin, 2006). The role of reading and writing direction of an individual's fi rst language (native reading direction) in cognitive tasks has not yet been agreed upon.…”

The effect of hand movements on numerical bisection judgments in early blind and sighted individuals

“…The aim of this study was to shed further light on this issue. In a prior study by our group carried out in sighted participants, we found that hand movements performed in the left peripersonal space (irrespective of the hand used) accentuated underestimation (i.e., a leftward bias) in numerical bisection, whereas movements in the right peripersonal space (irrespective of hand used) had the opposite tendency (Cattaneo, Fantino, Silvanto, Vallar, & Vecchi, 2011). These results suggest that the correspondence between physical space and the mental number space in sighted individuals is anchored to a world-based reference frame centered on the participants’ body (i.e., left in physical space and left on the mental number line).…”

“…The experimental task consisted of a numerical bisection paradigm that has been used in a number of prior studies to investigate spatial attentional biases in numerical representation (e.g., Cattaneo, Fantino, Silvanto, Tinti, & Vecchi, 2011; Göbel, Calabria, Farnè & Rossetti, 2006; Loftus, Nicholls, Mattingley, Chapman & Bradshaw, 2009). Participants were verbally presented with a total of 80 different pairs of three-digit numbers; half in ascending (e.g., “117 166”) and half in descending order (e.g., “959 934”).…”

“…Conversely, a rightward and upward change in eye position predicted that the next number would be larger than the last. At the same time, moving the hand in the left space (Cattaneo, Fantino, Silvanto, Vallar & Vecchi, 2011) or turning the head leftwards (Loetscher, Schwarz, Schubiger & Brugger, 2008) biases attention to small numbers, with the reverse tendency for hand movements or head towards the right. Although it is important to stress that the mental number line can be evoked based on a purely attentional basis without any obvious motor component (Nicholls, Loftus, & Gevers, 2008), the analogies consistently reported between movements along the mental number line and physical space suggest that our mental representations may be grounded, at least to a certain extent, in sensorimotor experience (Fischer, 2012).…”

“…The lack of prior visual experience has led to mixed reports in terms of its effect on the representation of external space and (at least to a certain extent) on the mental representation of numerical magnitude (Crollen, Dormal, Seron, Lepore & Collignon, 2013; Pasqualotto, Taya & Proulx, 2014). For example, prior evidence has found that blind individuals also tend to represent numbers in the form of a mental number line (Castronovo & Seron, 2007; Cattaneo et al, 2010; Szűcs & Csépe, 2005) showing attentional biases similar to those of sighted individuals when exploring it (Cattaneo, Fantino, Silvanto, Tinti & Vecchi, 2011). However, blind individuals may use different reference frames in representing numbers compared to sighted individuals, at least in certain experimental conditions.…”