Chapter 2. Prehension

Chapter 6 - During Contact 233
Table 6.2 The relationship between sensory modality and object
properties. While one EP seems to be stronger in extracting
information, others secondarily encode the information.
EP=exploratory procedure. From Lederman and Klatzky (1987) and
Klatzky and Lederman (1987).
Object Primary Modality Secondary EPs
Property EP
Texture lateral
motion
spatial density:
vision
mug h n e s s :
contour following
enclosing
static contact
haptics
Hardness pressure haptics enclosure
lateral motion
contour following
Temperature static
contact
haptics enclosure
contour following
Weight unsupported haptics
holding
enclosure
contour following
Volume enclosing vision static contact
(or size) unsupported
holding
contour following
Exact Shape contour
following
vision
Global shape static
contact
vision contour following
unsupported
holding
enclosure
human subjects lift objects in a two fingered pad opposition,
microslips (small movements of the object against the skin) occur that
are below the level of conscious awareness. The fingers continue to
apply pressure until these microslips disappear, suggesting that the
CNS adjusts to the ongoing frictional conditions (due to state of the
distal pulps, surface texture, contact area and object weight) as long as
the muscles are set for some range of values.
The relationships between object properties and how subjects get
the sensory information needed for a specific task (Table 6.2) have
been identified (Klatzky & Lederman 1987; Klatzy, Lederman, &
Reed 1987). Texture is better found haptically than visually, although
both encode them well, because texture has two components (spatial
density which is more accessible to vision, and roughness which is