Biomedical Engineering Reference
In-Depth Information
points of contact with a surface of support, and (b) physical contact with objects
in one's environment. When acquired actively, and in conjunction with kinesthetic
information (discussed below) this latter source of somatosensory information is
known as
haptics
, a topic that we discuss briefly below.
The other external senses likely have a negligible impact on the acquisition of
environmental knowledge. In theory, one can pickup somatosensory information
from external sources and use variations in the strength of these sources to navigate
or to inform one about the environment. For example, direct sunlight may heat one
side of a person more than another, allowing her to determine the direction of the sun
and, by extension, her orientation. Similarly, the strength of vibrations under one's
feet may be used to estimate one's proximity to a large machine on a factory floor.
Indeed, the fact that vibratory devices have been constructed to signal directions
for navigation [
108
] indicates that such information sources may be useful in some
circumstances. However in most everyday situations, the role of these and other
sensory systems (such as olfaction and taste) in environmental cognition is probably
minimal and is certainly not well researched.
1.2 Internal Sensory Information
Idiothetic information about space derives from three principal sensory systems: (a)
the vestibular system, which senses angular and linear acceleration of the head; (b)
the kinesthetic/proprioceptive system, which provides information about the position,
orientation, and movement of the musculature; and (c) the somatogravity system [
66
]
that informs people about the direction of gravity. A fourth source of information,
efference copy, is sometimes considered a source of idiothetic information [
67
];
however, we will defer discussion of efference copy to our discussion below of
efferent information more generally. The vestibular and kinesthetic/proprioceptive
systems have direct and important ties to spatial cognition, and we discuss them
briefly below; however, we do not discuss further the somatogravity system, as it is
little researched in humans, and its contributions to environmental knowledge are
largely unknown.
The anatomical basis of the vestibular system is a set of structures in the inner ear—
otoliths and semicircular canals—that sense linear and angular acceleration, respec-
tively. In addition to supporting several postural and oculomotor reflexes, vestibular
information provides information that can be doubly-integrated in order to deter-
mine linear or angular displacement. In this way, it is thought to provide a critical
input to people's ability to dead reckon and to update (see [
77
]). In the experimen-
tal literature, vestibular information is typically isolated by passively transporting
blindfolded participants; however, we note that such procedures do not completely
isolate the vestibular sense, as they do not remove somatosensory information about
inertial forces (e.g., the sensation of the wheelchair pressing against one's back).
These experiments have demonstrated that vestibular information enables better than
chance accuracy on online spatial tasks such as turn and distance estimation [
7
,
38
,
