Chapter 6 – Perception:
-The Brain receives fragment of information from aprx 1 million axons of each of the optic
nerves. It combines and organizes these fragments into perception of a sense.
Perception is the process by which we recognize what is represented by the information
provided by our sense organs. This process gives unity and coherence to this input.
Perception is a rapid, automatic, unconscious process; we puzzle out the meaning of what we
see. We do not see an object and then perceive it, we simply perceive the object.
The vision or the optical system is we considered to perception because of the richness of the
information provided by our visual system that is reason they focus on the explicit difference of
perception and our visual sensation.
Brain Mechanism of Visual Perception:
Circuits of neurons analyze particular aspect of visual information and send the results of their
analysis to another circuit, which perform further analysis and eventually leads the to
perception of the scene and all object in it. When it encounters it more, it will memorizes and be
familiar to object and learn the appearance.
Primary Visual Cortex:
Earliest stage of visual analysis has come from our investigation of the activity of individual
neurons in the thalamus and the primary visual cortex.
David Hubel and Torsten Wiesel conducted a test by inserting microelectrodes into visual
system of a cat. They concluded that the geography of the visual field is retained in the primary
Module consists of a black of tissue in size contain approximately 150 000 neurons. They found
that each module analyzed various characteristic of their own particular part of the visual field
that is their receptive field.
The Visual Association Cortex:
- For us to perceive objects and entire visual scenes, the information from these individual
modules must be combined. The combination takes place in the visual association cortex.
Two Streams of Visual Analysis:
- Visual information analyzed through the primary visual cortex and is further analyzed in the
visual association cortex.
- Regions are arranged in hierarchically, as circuit’s sends information, the detail would be keep
- The visual association cortex divides into two pathways: the ventral streams and dorsal s
stream. The ventral stream continues forwards and ends in the inferior temporal cortex. The
dorsal stream ascends into the posterior parietal cortex. The ventral stream recognizes what the object is, what form and what colour is it. The dorsal stream identifies where an object is
located is whether is moving.
The Ventral stream: perception of form:
- The recognition of visual patterns of and identification of particular objects takes place in the
inferior temporal cortex. The analyses for form and colour are put together and perception of
the three dimensional object emerge.
- Brain damage can cause a category of deficits known as visual agnosia. Agnosia refers to an
inability to perceive or identify a stimulus that exists with a specific sensory modality. (unable to
identify an object)
- A common symptom of visual agnosia is prosopagnosis, the inability to recognize particular
- People with brain damaged people and functional image studies indicate that the face –
recognizing circuits are found in the fusiform face area (FFA), a region of the ventral stream
located at the base of the brain.( not only face other stuff too.)
- Extrastriate body area (EBA) is specifically activated by photographs that respond to form
resembling the human body.
- Parhippocampal place area (PPA) is activated by visual scenes and background. Damaged
ventral stream that result in profound visual agnosia for object.
The Ventral Stream: perception of Colour:
- Some region is involved in combining the information from red/green and yellow /blue signals
that originate in retinal ganglion cells.
- Cerbral achromatopsia – the inability to discriminate among different hues; caused by damage
to the visual association cortex. If brain damage occurs on only one side, than they will lose
their colour vision in half the visual field. If it’s bilateral then they will lose all colour recognition
The Dorsal Stream: Perception of Spatial Location:
- Parietal lobe receives visual, auditory, somastosensory, and vestibular information is involved in
spatial and somastosensory perception. Disruption to parietal lobe will cause perceiving and
remembering the location of objects and control the movement of eyes and the limbs. Dorsal
stream is located posterior parietal cortex.
- Goodale suggested the primary function of the dorsal stream is to guide actions rather than
simply to perceive spatial location.
- Goodale con