L7 - Sensation and Perception 1 Flashcards
Sensation and Perception:
It is hard to draw the line between the two
- Sensation: the process by which sense organs gather information from the environment and transmit to the brain for initial processing
- Perception: turning this information into a representation of the world by selecting (relevant v irrelevant), organising and interpreting sensations
Naïve Realism=
The mistaken notion that perception is a veridical experience of the physical world…
Transduction =
The retina contains photosensitive structures that convert electromagnetic radiation (light) into electrochemical (neural) energy.
We have a blind spot that we don’t notice
Perceptual filling-in:
There are several reasons people don’t notice their blind spots - the most interesting is that the human visual system seems to assume that the same things that surround the blind spot are also within the blind spot
The motion aftereffect:
The motion aftereffect is characterised by a visual sensation generated entirely within the visual system!
It demonstrates that…
- We don’t directly see images that project to your retinae
- We cannot see what we know to be true – you know an image is static, but still experience illusory motion
- Perception can result from subconscious processes, not controllable by volition
Binocular Rivalry:
Binocular rivalry can occur when different images are shown to the two eyes…
It is characterised by…
- Perceptual suppression
- Changes in perceptual dominance
Selective Visual Attention:
We do not experience all information available to us equally. We selectively prioritise information processing, and this modulates perception.
The Primary Visual Cortex:
- First cortical brain region to receive visual input
- Often called V1
- V1 damage can cause people to report a complete loss of visual sensation for specific regions of space – a cortical scotoma
- There is one V1 in each half of the
brain. Each encodes information from the opposite side of visual space
Chromatic Flicker:
A light can change between red and green at different rates. At fast rates, we cannot see red or green – just yellow. At slower rates we can see red and green, but not yellow
Sub-conscious V1 activity…
might not shape perception, but could contribute to other visual operations.
Evidence for a vision / action dichotomy:
The dual visual streams hypothesis:
D.F. can prepare appropriate manual responses for visual stimuli she cannot name.
This has been taken as evidence for separate dorsal and ventral visual pathways, respectively important for object manipulation and object recognition
Blindsight =
when people display evidence of visual sensitivity, but insist they cannot see.
If people report being‘blind’ but can perform visual tasks – how can we measure their residual sensitivity?
We can adopt Signal Detection Theory – this theory describes how to measure sensitivity to physical inputs under conditions of uncertainty…
Signal detection theory:
Measures of performance which can be derived from a response matrix
-
Sensitivity: What is the minimal signal that can be discerned from background noise? (measured by D)
- E.g. Two doctors with same training can both pick out a tumour
-
Criterion: What is the internal decision process that determines when a signal is sufficient to sound the alarm? (how much evidence do you need to confidently say that you can see the signal?)
- E.g. Two doctors may be more or less conservative when it comes to making a decision that it is a tumour
-
Iso-sensitivity (ROC) curves
- D-prime (d’): Sensitivity of the perceptual system to distinguish a signal from noise
- c: Index of a person’s willingness to say “yes, the target was present”
- Motivation can affect sensitivity: e.g. if you are given $1 for every hit, you will have far more hits and false alarms than if you have to pay $1 for each false alarm
The Binding Problem:
The binding problem refers to the apparent need to integrate activity from multiple brain structures and is best characterised as a spatial and timing dilemma
