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Perception, Attention and Decision Making (PADM) Summary
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Summary of all the lecture of the PADM course of Brain and cognition minor.
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PERCEPRION, ATTENTION &DECISION MAKING
PERCEPTION
Perception starts with sensations: except the 5 senses that are commonly known (sight, hearing, smell, taste,
touch), we can sense a lot more specialized things, with specialized receptors that we have in our bodies:
thermoreceptors, proprioception (presence of the body), nociception (pain), equilibrioception, mechanisation,
stretch receptors, chemoreceptors, chrono-receptors, electroception, polarized light receptors.
VISION & VISUAL SYSTEM
The human visual system is limited. This means that our perception of the world is limited too, since it heavily
depends on the sense of vision. For example, the electromagnetic spectrum of colour is vast, but we can only
perceive a very small part of that.
THE VISUAL PATHWAY
A misconception is that the information
from each eye crosses to the other
hemisphere. This is not true (see graph).
What happens is that each hemisphere
collects information from the opposite
visual field, and a visual field consists of
the same side of each of the retinas.
Information from the optic nerve crosses
over via the optic chiasm. The lateral
geniculate nucleus (LGN) is important in
visual processing and perception: it is a
relay centre in the thalamus for the visual
pathway. The path from LGN to the
primary visual cortex is the primary
visual pathway (genicular-striate).
OTHER VISUAL PATHWAYS
There are approximately 10 secondary visual pathways in the human
brain:
- Suprachiasmatic nucleus (hypothalamus): interpretation of
light, maintenance of body clock (jetlag and phones).
- Superior colliculus: eye and neck movements (related to
reflexes).
They are all older pathways; their functions seem to be more
necessary for evolution.
,SPLIT-BRAIN PATIENTS, BLINDSIGHT AND AKINITOPSIA
Split brain patients are the people who have had their hemispheres surgically separated as a treatment for
epilepsy. The corpus callosum that connects the two hemispheres is removed. This means that the two
hemispheres do not really ‘communicate’ with each other, thus information from the environment is still
processed but it does not cross over.
- When a split-brain patient is asked what they see they will mention only what they see on the right
visual field, since the left hemisphere is what perceives the right visual field and also the one
responsible for language.
- When a split-brain patient is asked to grab something, they do so with their left hand.
- Patients confabulate to make sense of actions that are promoted by the right hemisphere.
Blindsight: acquired damage to the V1 (primary visual area). These patients get a diagnosis of blindness, but
they can still make accurate visual discriminations in the field in which they are blind. This tells us a lot about
conscious perception. These patients are an indication that perception is not only conscious, but also
unconscious. Blindsight patients can detect motion without consciously seeing the object.
Akinetopsia (motion blindness): acquired damage in the V5 (visual area related to motion detection). These
people cannot detect stimuli that move, but they can still detect biological motion. The area that is related to
detection of biological motion is the posterior STS (also important to eye gaze), which is placed very close to
V5.
THE VISUAL CORTICES
The visual cortices seem to be specialized in different
properties of visual stimuli (colour, shape, motion
etc).
THE VISUAL PROCESSING STREAMS
1. Dorsal stream (where): guided voluntary top-
down control, specialized in spatial placement
and recognition of stimuli and objects in space.
Damage to this stream leads to hemi-spatial
neglect, meaning that half of the visual field of
the patients is neglected.
2. Ventral stream (what): this stream is
responsible for detecting unattended and
unexpected stimuli in the visual field, and it is
concerned with understanding the nature of
these stimuli or objects. Damage to this stream
leads to alexia (not be able to read words) or
prosopagnosia.
, OBJECT RECOGNITION
Gestalt principles: theory of perception of how we group elements of visual stimuli, recognize patterns and
simplify complex images.
MARR’S THEORY OF VISION
Recognition of an object relies on recognition of its parts/features.
RIDDOCH & HYMPHERY’S THEORY
The object is seen, and then all its forms are broken down and recognized.
After that the elements are combined to construct individual shapes. Then
these are matched to mental representations of the object we have in our
heads.
View normalization: objects are rotated and manipulated mentally to fit
the principal axis representations we have stored in memory. When this
process is done then we can match the mentally manipulated image to
concepts we have in our heads.
When size and orientation of objects are changed, the right fusiform
gyrus and the right posterior parietal lobe are more active for orientation
change, so additional complexity and computation are done there. The
left fusiform gyrus is responsible for the direct route (no change in
shape/rotation).
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