Haptic perception in virtual reality in sighted and blind individuals
The incorporation of the sense of touch into virtual reality is an exciting development. However, research into this topic is in its infancy. This experimental programme investigated both the perception of virtual object attributes by touch and the parameters that influence touch perception in virtual reality with a force feedback device called the PHANTOM (TM) (www.sensable.com). The thesis had three main foci. Firstly, it aimed to provide an experimental account of the perception of the attributes of roughness, size and angular extent by touch via the PHANTOM (TM) device. Secondly, it aimed to contribute to the resolution of a number of other issues important in developing an understanding of the parameters that exert an influence on touch in virtual reality. Finally, it aimed to compare touch in virtual reality between sighted and blind individuals. This thesis comprises six experiments. Experiment one examined the perception of the roughness of virtual textures with the PHANTOM (TM) device. The effect of the following factors was addressed: the groove width of the textured stimuli; the endpoint used (stylus or thimble) with the PHANTOM (TM); the specific device used (PHANTOM (TM) vs. IE3000) and the visual status (sighted or blind) of the participants. Experiment two extended the findings of experiment one by addressing the impact of an exploration related factor on perceived roughness, that of the contact force an individual applies to a virtual texture. The interaction between this variable and the factors of groove width, endpoint, and visual status was also addressed. Experiment three examined the perception of the size and angular extent of virtual 3-D objects via the PHANTOM (TM). With respect to the perception of virtual object size, the effect of the following factors was addressed: the size of the object (2.7,3.6,4.5 cm); the type of virtual object (cube vs. sphere); the mode in which the virtual objects were presented; the endpoint used with the PHANTOM (TM) and the visual status of the participants. With respect to the perception of virtual object angular extent, the effect of the following factors was addressed: the angular extent of the object (18,41 and 64°); the endpoint used with the PHANTOM (TM) and the visual status of the participants. Experiment four examined the perception of the size and angular extent of real counterparts to the virtual 3-D objects used in experiment three. Experiment four manipulated the conditions under which participants examined the real objects. Participants were asked to give judgements of object size and angular extent via the deactivated PHANTOM (TM), a stylus probe, a bare index finger and without any constraints on their exploration. In addition to the above exploration type factor, experiment four examined the impact of the same factors on perceived size and angular extent in the real world as had been examined in virtual reality. Experiments five and six examined the consistency of the perception of linear extent across the 3-D axes in virtual space. Both experiments manipulated the following factors: Line extent (2.7,3.6 and 4.5cm); line dimension (x, y and z axis); movement type (active vs. passive movement) and visual status. Experiment six additionally manipulated the direction of movement within the 3-D axes. Perceived roughness was assessed by the method of magnitude estimation. The perceived size and angular extent of the various virtual stimuli and their real counterparts was assessed by the method of magnitude reproduction. This technique was also used to assess perceived extent across the 3-D axes. Touch perception via the PHANTOM (TM) was found to be broadly similar for sighted and blind participants. Touch perception in virtual reality was also found to be broadly similar between two different 3-D force feedback devices (the PHANTOM (TM) and the IE3000). However, the endpoint used with the PHANTOM (TM) device was found to exert significant, but inconsistent effects on the perception of virtual object attributes. Touch perception with the PHANTOM (TM) across the 3-D axes was found to be anisotropic in a similar way to the real world, with the illusion that radial extents were perceived as longer than equivalent tangential extents. The perception of 3-D object size and angular extent was found to be comparable between virtual reality and the real world, particularly under conditions where the participants' exploration of the real objects was constrained to a single point of contact. An intriguing touch illusion, whereby virtual objects explored from the inside were perceived to be larger than the same objects perceived from the outside was found to occur widely in virtual reality, in addition to the real world. This thesis contributes to knowledge of touch perception in virtual reality. The findings have interesting implications for theories of touch perception, both virtual and real.