The objective of the present study was to explore cross-modal associations between color and tactile sensation while using haptically rendered virtual stimuli with substance properties of roughness/smoothness, hardness/softness, heaviness/lightness, elasticity/inelasticity, and adhesiveness/ nonadhesiveness. The stimuli with the indicated properties were rendered with the aid of SensAble PHANTOM OMNI® haptic device. The experimental setup required the participants to use exploratory procedures typical to real object interaction, and select a color from the HSV color space that matched the experienced sensation. The findings of our investigation reveal systematic mapping between color characteristics and intensity of the haptic stimuli. Qualitatively different haptic sensations, however, produced relatively similar patterns of cross-modal associations.

Cross-modal associations refer to non-arbitrary associations of features across sensory modalities. Such associations have been observed between many different sensory features. One association that has rarely been studied so far is between touch and color. In this study, participants were asked to match tactile and haptic adjectives to color samples shown individually on a screen. They could select one to 11 tactile and haptic terms, presented in 11 pairs of opposed adjectives. The results showed a regular pattern in the way tactile and haptic terms were matched to color. Our results further revealed that the colors to which tactile and haptic terms were matched did not fall within the boundaries of color lexical categories, suggesting that the associations were not based on lexicon — despite the frequent occurrence of linguistic expressions such as ‘soft pink’, not all colors called ‘pink’ were matched to ‘soft’. In contrast with one recent study, the distribution of tactile and haptic terms across the Munsell array suggests that along with brightness and chroma, hue was also relevant to participants’ responses. Specifically in the case of hue, several opposed adjectives were relatively well matched to opposed colors, along the orthogonal Yellow/Blue and Red/Green axes, which are suggested to structure the space of hue experience. Possible accounts of these results are considered.

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The present study undertakes an ecological approach to haptic interfaces grounded in the sense of agency that accompanies human action. The study had two aims. The first aim was to investigate the effect of two top-down cues (perceived initiation of action and presence of action options) on sense of agency in haptic interfaces. The second aim was to investigate the consistency of the sense of agency and answer the question whether consistent force feedback (bottom-up cue) is sufficient to grant stable experience of agency. The results of the study suggest that while high number of action options can be associated with stronger agency, low numbers of action options are unlikely to produce such effect, and that the cue of task completion might be critical for the sense of agency. The study also showed that sense of agency was relatively inconsistent, with the main source of uncertainty being computer-attributed agency. The discussion addresses issues of joint human-computer agency and the contribution of multiple sources of information to agency experience.