intro Flashcards
Vision system is not a camera
We use our eyes for perception and to generate meaningful and adaptive representations of the environment
Craik-O’Brien Cornsweet Effect - Why do our brains see it differently to cameras?
Camera will only perceive the illusion as one grey level due to no difference in hue
Our visual system will ignore the light intensity because it wants to generate meaningful reasons as to why it looks different
Tabletop illusion
We aren’t interested in the context behind the items but our eyes identify them as 3D objects and think they are different sizes despite them being the same
Optics and reverse optics
Inverting the optical and perceptive process is hard, our brain relies on context in order to understand the world around it
Retina
Retina is the sheet of sensory neurons at the back of the eye that pick up light or light intensity
Two toned image and context
Without context, the image looks confusing, but when context is presented (horse kissing) then we know what it is - binding meaning into the perceptive process
Information processing paradigm
Brain processes 2D input and transforms it into a meaningful 3D interpretation of the world
Why measure threshold limits
By understanding the limits of perception we can make inferences of how the visual and perceptual system works
Absolute threshold
Smallest amount of stimulation that can be reliably detected
Difference threshold
Smallest difference between two stimuli that can be reliably detected
How to test absolute threshold
2-alternative forced choice task
Show participant two stimuli and ask which of the two has pattern
As contrast reduced, can see the point where participant is just able to see difference
Threshold mapping for absolute threshold
Soft threshold rather than hard threshold
Characterised in seeing the level in which participant reaches certain performance level
“What contrast do we need to show them so they are always 75% able to guess correctly”
How to test difference threshold
One stimulus called reference and one called comparison
Reference held at fixed level of intensity
Ask participant which pattern has a higher contrast
Contrast changes in comparison until the participant is just able to see the difference between the two
Threshold mapping for difference threshold
If the contrast of the comparison is much lower than the reference then the participants will almost never choose the comparison as higher contrast
Soft thresholds again
Just Noticeable Difference
Difference in intensity that a participant is able to see
