@article{lacey-peters-sathian-07_cross-modal-object-recognition-viewpoint,
  title={Cross-modal object recognition is viewpoint-independent},
  author={Simon Lacey and Andrew Peters and K. Sathian},
  journal={PloS one},
  volume={2},
  number={9},
  pages={e890},
  year={2007}

Background
Previous research suggests that visual and haptic object recognition are
viewpoint-dependent both within- and cross-modally. However, this conclusion
may not be generally valid as it was reached using objects oriented along
their extended y-axis, resulting in differential surface processing in vision
and touch. In the present study, we removed this differential by presenting
objects along the z-axis, thus making all object surfaces more equally
available to vision and touch.

Methodology/Principal Findings
Participants studied previously unfamiliar objects, in groups of four, using
either vision or touch. Subsequently, they performed a four-alternative
forced-choice object identification task with the studied objects presented
in both unrotated and rotated (180° about the x-, y-, and z-axes)
orientations. Rotation impaired within-modal recognition accuracy in both
vision and touch, but not cross-modal recognition accuracy. Within-modally,
visual recognition accuracy was reduced by rotation about the x- and y-axes
more than the z-axis, whilst haptic recognition was equally affected by
rotation about all three axes. Cross-modal (but not within-modal) accuracy
correlated with spatial (but not object) imagery scores.

Conclusions/Significance
The viewpoint-independence of cross-modal object identification points to its
mediation by a high-level abstract representation. The correlation between
spatial imagery scores and cross-modal performance suggest that construction
of this high-level representation is linked to the ability to perform spatial
transformations. Within-modal viewpoint-dependence appears to have a
different basis in vision than in touch, possibly due to surface occlusion
being important in vision but not touch.

}}


@article{norman-norman-04_visual-haptic-perception-of-natural-object-shape,
  title={The visual and haptic perception of natural object shape},
  author={Norman, J.F. and Norman, H.F. and Clayton, A.M. and Lianekhammy, J. and Zielke, G.},
  journal={Attention, Perception, \& Psychophysics},
  volume={66},
  number={2},
  pages={342--351},
  year={2004},
  publisher={Springer}

In this study, we evaluated observers’ ability to compare naturally shaped
three-dimensional (3-D) objects, using their senses of vision and touch. In
one experiment, the observers haptically manipulated 1 object and then
indicated which of 12 visible objects possessed the same shape. In the second
experiment, pairs of objects were presented, and the observers indicated
whether their 3-D shape was the same or different. The 2 objects were
presented either unimodally (vision–vision or haptic–haptic) or cross-modally
(vision–haptic or haptic–vision). In both experiments, the observers were
able to compare 3-D shape across modalities with reasonably high levels of
accuracy. In Experiment 1, for example, the observers’ matching performance
rose to 72% correct (chance performance was 8.3%) after five experimental
sessions. In Experiment 2, small (but significant) differences in performance
were obtained between the unimodal vision–vision condition and the two
cross-modal conditions. Taken together, the results suggest that vision and
touch have functionally overlapping, but not necessarily equivalent,
representations of 3-D shape.

}}