The human visual system is a complex variety of organs, sensors, and receptors that work together to detect and process the world around us. One part of this visual system is the dorsal stream.
The dorsal stream is one of two different cortical streams involved in visual processing. According to Bear, Connor, and Paradiso (2007) the dorsal stream of the analysis of visual movement, as well as the control of visual activity (p. 333). Kalat (2009) describes this as a “how” or “where” way because of its role in helping the motor system find and use various devices. Research done on macaque monkeys by Newsome and Stanford University colleagues (as in Urso, Connors and Paradiso, 2007) noted that electrical stimulation in area MT (the area that helps organize the dorsal stream) changed the perceived direction of the monkey. in which the lights are moved by small points (p. 335). This research suggests that stimulation of areas associated with a certain movement direction causes the brain to believe that it has sensed movement in that direction (i.e. stimulation in the “left” area creates a preferential perceptual movement in that area).
Kalat (2009) notes that individuals with brain damage with dorsal stream cannot “touch the object accurately, even after the size, shape, color” and “although they can remember what the object looks like, they cannot remember how it is arranged. This lack of ability to arrange things according to memory of one’s position also seems to transfer to other features, such as body parts, etc. One particular study confirming this concept was done by Goodale and Milner (1992) in a patient with brain damage is that it separated the connection to the dorsal stream, the patient experiencing the inability to indicate the dimensions of various objects, as indicated by the researchers (as qtd in Arbib, 2006). He could not consciously adapt to the situation ahead of time. Thus, the dorsal stream was called “how” to serve as a way for the body to move and interact with the world.
Damage to the dorsal stream, areas of the posterior parietal cortex and the superior parietal cortex, thus causing what is known as “optic ataxia.” Optic ataxia is a deficiency of the visuomotor system, which allows to resolve the ability to perform “directed goal actions to visual targets” with all precision and accuracy (Snider, et al., n.d). However, it is important to note that optic ataxia leaves the location (where) of the object induced, even though the individual is unable to perform accurate actions with the object.
Notes:
Arbib, M. A. (2006). Activity to Language through the Mirror Neuron System. New York: Cambridge University Press.
Bear, M. F., Connors, B. W., & Paradise, M. A. (2007). Neuroscience: Exploring the Brain, 3rd ed. Baltimore: Lippincott Williams & Williams.
Goldstein, E. (2007). Bell Mountain: Wadsworth.
Kalat, J. W. (2009). Biological Psychology. Bell Mountain: Wadsworth.
Snider, B., Arthur, S., Thompson, D., & LeSage, M. (N.d). Dorsal River Retrieved November 4, 2009, from http://ahsmail.uwaterloo.ca/kin356/dorsal/dorsal.htm
Werner, J., Chalupa, L. M. (2004). Visual Neurosciences, Vol. 1. Bakerville: Massachusetts Institute of Technology.
