Chapter 6: Perception
- Primary function of sense organs is to provide information to guide behaviour
- Perception: a rapid, automatic, unconscious process by which we recognize what is represented
by the information provided by our sense organs
Brain Mechanisms of Visual Perception:
- Visual perception by the brain is often described as a hierarchy of information processing
- According to this scheme, circuits of neurons analyze particular aspects of visual information
and send the results of their analysis to another circuit, which performs further analysis.
Eventually this process leads to perception of the scene and all objects in it.
The Primary Visual Cortex
- our knowledge of the earliest stages of visual analysis has come from investigation of the
activity of individual neurons in the thalamus and the primary visual cortex
- David Hubel and Torsten Wiesel inserted microelectrodes into various regions of the visual
systems of cats and monkeys to detect the action potentials produced by individual neurons.
The signals picked up by the microelectrodes are electronically amplified and sent to a recording
device for later analysis
- The anesthesia makes the animal unconscious but does not prevent neurons in the visual
system from responding.
- The researches moved a stimulus around on a large screen until they located the point where it
had the largest effect on the electrical activity of the neuron
- They concluded that the geography of the visual field is retained in the primary visual cortex.
That is, the the µ(}(Z]v]^u_}vZµ(}(Z]uÇÀ]µo}Æ
- They found that neural circuits within each module ( a block of cortical tissue that receives
information from the same group of receptor cells) analyzed various characteristics of their own
particular parts of the visual field t that is of their receptive field ( that portion of the visual field
in which the presentation of visual stimuli will produce an alternation in the firing rate of a
The Visual Association Cortex
- For us to perceive objects and entire visual scenes, the information from individual modules
must be combined which takes place in the visual association cortex
- Visual information analyzed by the primary visual cortex is further analyzed in the visual
- Neurons in the primary visual cortex send axons to the region of the visual association cortex
that surrounds the striate cortex. At this point, the visual association cortex divides into two
pathways: 1) the ventral stream 2) the dorsal stream
- Figure 6.2 page 172
1) the ventral stream: the flow of information from the primary visual cortex to the visual
association area in the lower temporal lobe; used to form the perception of an objects shape,