**6.1 Method**

88 Haptics Rendering and Applications

by the calibration hypothesis. Both functions seem to reflect a common underlying spatial

Fig. 10. Overall spatial bias in haptic perception of slant (Experiment 1) superimposed on

Using real surfaces with a demarcated axis of haptic exploration, we sought to extend the methods used by Durgin, Li and Hajnal (2010) to the haptic domain. Our results indicate a close correspondence between visual and haptic spatial biases in the peception of orientation. Our results are somewhat at variance with those of Hajnal et al. (2011). Because Hajnal et al. did not constrain the path of digital exploration, it is possible that participants tended to explore their surfaces along a somewhat oblique (and therefore less steep) axis. Our data are consistent with the proposal that there is a trend for there to be calibration

**6. Experiment 2: Horizontal/vertical bisection point for surface orientation in** 

To avoid verbal biases, Durgin, Li and Hajnal (2010) used a bisection task in which they presented surface visually and asked participants to indicate whether the surface was closer to vertical or to horizontal. They reported a mean visual bisection of point of 34° from horizontal. That is, a surface of 34° was equally likely to be judged closer to vertical as it was to be judged closer to horizontal. In fact the cubic fit to their verbal data predicted that the 45° point would have been at 36.3° in the visual case, and it seems likely that verbal reports tend to slightly underestimate the magnitude of the actual spatial bias (see also Durgin & Li, 2011a, 2011b). The present experiment simply replicated the bisection procedure of Durgin,

the visual slant bias function from Durgin, Li and Hajnal (2010).

between visual and haptic representations of 3D surface orientation.

**depth assessed by dynamic touch with the tip of the index finger** 

coding bias.

**5.3 Discussion** 

Li and Hajnal for the haptic case.

The haptic horizontal/vertical bisection point was measured.
