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Selective perception in probing by foot: Perceiving the length of a probe and the distance of a probed surface

Perception of properties of object wielded by means of muscular effort exhibits both task specificity and anatomical independence. A person can perceive different properties of an object wielded by a given anatomical component and can perceive a given property of an object wielded by different anatomical components. Task-specificity and anatomical independence are fundamental characteristics of the haptic system described a biotensegrity system embedded in lawfully structured energy arrays. We investigate whether both characteristics are also exhibited when a person attempts to perceive properties by means of a wielded object. Participants used a foot-wielded rod to probe a surface and reported the length of the rod and the distance of the surface probed (on separate sets of trials). The ability to differentiate these properties generalized across anatomical components, and perception of each property by foot was supported by sensitivities to the same invariant mechanical parameters that support perception of each property by hand. The results suggest that the biotensegrity hypothesis applies to perception both of and by means an object attached to the body.

Comparison of two psychophysical methods across visual and haptic perception of stand-on-ability

Recent research (Hajnal et al. in Perception 45(7):768-786, 2016) found apparent differences between haptic and visual perception of the affordance of stand-on-ability. One reason for this discrepancy might be the imprecision of the measurement method. We compared the psychophysical method of adjustment with a dynamic staircase method of stimulus presentation in an affordance task. Three groups of participants either visually inspected a flat sturdy sloped ramp, placed one foot onto the ramp occluded from view, or placed one foot on the ramp while allowed to look at it, in the visual, haptic, or multimodal condition, respectively. Each trial was presented by moving the ramp up or down until the participant perceived the action boundary, i.e., the steepest slope that still afforded upright stance. After perceptual trials, we measured the actual action boundaries by allowing participants to attempt to stand on the ramp. The action boundary was the average between the lowest false alarm and steepest hit within a 1.5° margin of difference. Visual perception was found to be equivalent with haptic perception. Perceptual and action boundaries were indistinguishable, but only when employing the more precise staircase method. The results support the postulate of equivalence among perceptual systems proposed by Gibson (The senses considered as perceptual systems. Houghton Mifflin Company, Boston, 1966), and the idea of correspondence between perception and action which is the cornerstone of affordance theory.

Is Perception of Stand-on-able-ness Equivalent Across Degrees of Dynamic Touch?

From the ecological perspective on perception and action, objects and events structure patterned energy distributions such that this structure is specific to its source. Moreover, such structure is invariant over transformations and over particular instances of perceiving. Therefore, the ability to perceive a given functional property is potentially equivalent across both different perceptual modalities and different configurations of the same perceptual modality. We investigated whether this is the case for perception of affordances of a surface that is explored with a part of the body in different contexts. Specifically, we investigated perception of whether an inclined surface could be stood on when the participant explored that surface by stepping onto it with and without bearing weight on the foot. Analyses of the proportion of “yes” responses, the steepest slope angles that were perceived to afford upright stance, and the steepest slope angles that afforded upright stance revealed no differences between perception across the 2 conditions. In particular, there was no difference in perceptual boundaries across the 2 conditions, and neither of these was different from the behavioral boundary. Our findings support the hypothesis that the stimulation patterns supporting perception are invariant across degrees of exploration and are consistent with the hypothesis that the haptic perceptual system is organized as part of a complex biotensegrity system.