Environmental Engineering Reference
In-Depth Information
was most pronounced in middle age adults, but weakly present in all age groups. While
there are many directions to head with future research, the finding regarding the possibility
of performance enhancement through the manipulation of luminance contrast is one
particular area of interest.
4. Future directions
In the final sections, we will develop a theoretical basis for the importance of understanding
the role of luminance contrast for precise, visually guided movements of the upper
extremities. Following this, we briefly describe our next set of experiments aimed at a
deeper understanding of the role of vision for motor performance in virtual environments
across the lifespan.
4.1 Contrast sensitivity and tuning of neuronal populations
The neural processing of sensory information is described by the tuning of neuronal
populations to specific stimuli (Desimone & Duncan, 1995). Within areas of the visual cortex,
groups of neurons fire in response to the presence of afferent information. This firing rate is
tuned to specific aspects of the stimulus, thereby increasing the precision by which the system
can differentiate visual information. Within neuronal populations, firing rates differ among
neurons. Some neurons will fire constantly with the presence of a stimulus, known as tonic
firing. Other neurons fire rapidly at the onset of the stimulus, and rapidly decrease activity
thereafter; this is known as phasic activity. This phasic activity makes the general sensorimotor
system particularly sensitive to changes in stimulation. The visual cortex is no exception.
Phasic neurons located within the visual cortex are sensitive to areas within the visual scene
that are actively changing. It is simple to understand this in the case of a moving object,
however the border of a stationary object also has this effect. Specifically, when the eye is
moving and a stationary image passes over the moving retina, the border of the stationary
object causes the visual scene to abruptly change, and phasic neurons react accordingly.
Sensitivity to object borders is dependent on the visual contrast between the object and its
background. Contrast is described by two characteristics, luminance (brightness) and
chromaticity (color), which are processed differently in the dorsal and ventral visual
streams. The two visual stream hypothesis put forth by Goodale and Milner has a wide
breadth of experimental support in explaining multiple functions for visual processing
(Goodale and Milner 1992 as cited in Milner & Goodale, 2008). Briefly, the ventral stream
includes structures along the pathway from the visual cortex in the occipital lobe to the
inferotemporal lobe. This circuit has been implicated in the use of vision for perception of
the surrounding environment, allowing the conscious experience of seeing the world
around us. The dorsal stream includes the pathway from the visual cortex to the posterior
parietal lobe. This pathway is responsible for the visuomanual transformations that allow
visual information to guide our motor system in interacting with the surrounding
environment. The neuronal structure of the ventral stream allows for high spatial resolution
and sensitivity to chromaticity (Wade et al., 2002). Processing of color information in the
ventral stream plays a role in the perception of objects (Kleinholdermann et al., 2009;
Morrone, Denti, & Spinelli, 2002). The role of color contrast in visual processing for motor
output has not been clearly elucidated, but it appears the strict dichotomous notion of the
