On Haptic Cues, Dimensions, and Stability in Touch

Haptic perception plays an integral role in how we interact with and make sense of the physical world. As research in this domain continues to expand across disciplines, conceptual ambiguities in terminology and theoretical frameworks persist. In this review, I address several of these ambiguities by proposing explicit accounts of notions often used implicitly in haptic research. Following a brief overview of the physiological and mechanical foundations of skin-object interactions and the somatosensory system, I introduce working definitions for terms such as haptic cues, stimuli, and perceptual dimensions, along with related assumptions and misconceptions. I argue that the distinction between distal and proximal stimuli or cues - more commonly applied in visual perceptual psychology - can serve as a helpful framework in haptic research for distinguishing physical (object-level) and mechanical (interaction-level) inputs. I then review some of the most commonly studied haptic dimensions, including stimulus magnitude, shape, material and texture, motion and time, weight, and size, along with the cues thought to inform them. This is followed by an examination of the notion of stability in haptic perception - often referred to as constancy or invariance - and its relevance for understanding how the sensory system creates consistent and behaviorally relevant percepts under variable conditions and cues. The specific phenomenon of perceptual and sensory metamers is explored as a particularly compelling example of cue integration and perceptual stability. I then address the various levels at which haptic stimuli and cues can be manipulated in research. Finally, I consider implications for haptic technologies and virtual environments as well as future directions. This conceptual framework aims to reduce terminological ambiguity and advance a clearer account of how stable haptic percepts are achieved.