Chapter 6: Sensation and Perception: Vision
Organization of Sensory Systems
- Sensation: the detection of some aspect of a stimulus in the environment
- Perception: the way in which we (or our brains) interpret the information that is
gathered by the senses
- The primary sensory cortex: the first part of the cortex that receives information relayed
from the senses through the thalamus. It was the most direct access to the information
provided by the sensory systems (eyes). The primary sensory cortex sends this
information to secondary cortical areas.
- The secondary sensory cortex: highly interconnected, and thus the secondary sensory
cortex also receives information from other areas of the secondary sensory cortex. It
sends its information to the association cortex.
- The association cortex: receives information from more than one sense.
Senosry systems are characterized by hierarchal organization
Each level of the organization contains functionally distinct cortical areas
The processing of sensory information occurs in parallel throughout the cortex
- Eye: large number of very specialized receptors that have one function (light – signals)
- Association cortex: more complex, integrate information from a number of sensory
systems into a perception of the outside world
- Sense organ – thalamus – primary sensory cortex – secondary sensory cortex –
association cortex (however parallel processing is more interconnected throughout the
Segregation by Function
- All areas are not processing the same kind of information.
- This type of functional segregation occurs at all three levels of the cortex in sensory
Processing of Information in Parallel
- Information is transmitted throughout the sensory system in parallel, each level
receiving some information from the level immediately below it and some from levels
- Allows information to flow rapidly and decreases the reliance of the system on any one
level of processing.
The Visual System
Light: Stimulus for the Visual System Chapter 6: Sensation and Perception: Vision
- Electromagnetic (EM) energy exists in a wide range of frequencies, and at 400-700
nanometres, EM energy is visible to the human eye.
The Eye and Retina
- Light enters the eye through the pupil and is focused on the retina by the curvature of
the cornea and fine-tuned by the lens.
- The retina is a layered structure at the back of the eye that contains 5 different types of
cells (receptors, horizontal cells, bipolar cells, amacrine cells, and retinal ganglion cells)
each of which has a different function
- The largest and most thoroughly studied visual pathway which begins in the eye and
ends in the primary visual cortex
- The Lateral Geniculate Nucleus of the Thalmus:
The LGN is a 6 layered nucleus of the thalamus that receives information from the
o P pathway responsive to colour, detail, and stationary/moving objects (cones)
o M pathway responds to movement and orientation but does not respond to
color or detail (rods)
- Striate Cortex: the visual cortex is also known as the striate cortex, because when it is
viewed under a microscope it has a strip