Du stimulus au Percept : éléments, mécanismes et stabilité dans la perception haptique

Haptic perception serves as our primary interface to the physical world. Without it, our ability to understand and respond to a world full of objects and subjects would be profoundly impaired. This dissertation addresses the problem of how we perceptually reconstruct what is in contact with our skin from behaviorally-relevant mechanical inputs during haptic interactions. Behaviorally-relevant information is defined as the kind of information that allows the sensory system to achieve its goals, and a primary goal of the somatosensory system is to enable the exploration and dexterous manipulation of objects.Following an introduction (Chapter 1), which covers fundamental concepts related to the emergence of stable haptic percepts, the dissertation comprises a series of experimental studies aimed at uncovering the essential cues and mechanisms used to perceptually reconstruct different haptic interactions. Because most haptic interactions start with the detection of contact, the first challenge taken in Chapter 2 is to identify what information the sensory system uses to detect the onset of skin contact during basic impact events. This first part of the dissertation uncovers a basic intensity metamer in the encoding of impact events and suggests the total amount of energy transferred by a force (i.e., the mechanical work) as an important cue, but not the sole determinant in the perceptual decomposition of haptic skin-object interactions.The focus then moves towards more complex everyday-like skin-object interactions. Because texture and material cues are critical to grasp and sliding behavior, special emphasis is placed on haptic texture and material perception (i.e., roughness and compliance perception), spanning three full chapters of this dissertation. Given the high-dimensional nature of haptic material and texture perception, Chapter 3 first explores how we can capture the complexity of haptic interactions with naturalistic surfaces without compromising on the experimental control needed to link specific cues to perceptual phenomena. This problem is addressed via the development of a dual-property stimulus database containing well-characterized stimuli which resemble the statistics of naturally occurring rough and compliant surfaces.In a following experiment, Chapter 4 then explores the contribution of vibratory propagation waves in perceptually reconstructing these surfaces by eliminating cutaneous information using local anesthesia of the index finger. We identify propagation waves as a behaviorally-relevant and sufficient cue for roughness perception for some, but not all participants. The perceived softness of these surfaces, on the other hand, is strongly diminished when local tactile information is removed. Subsequently, Chapter 5 explores the combined influence of surface features and material elasticity in mediating roughness and softness perception and highlights a perceptual confound in the reconstruction of surface roughness. The work uncovers roughness metamers, that is, regions where different cue combinations lead to identical perceptual outcomes.The final empirical chapter of this dissertation (Chapter 6) uncovers the consequence of the perceived timing of dynamic haptic interactions when behaviorally-relevant local tactile cues are removed. A temporal-binding task is used to illuminate the role of cutaneous cues in estimating the time course of mechanical skin-button interaction.Together, the work presented in this dissertation highlights the importance of correctly determining the contributions of physical, mechanical, neural, and perceptual-level cues and mechanisms in understanding the reconstruction of our world of touch.