Some quick revision!

Perception: Visual Illusions

Hermann Grid

One explanation! One explanation of the appearance of grey ‘blobs’ is based on receptive fields We only tend to see the blobs in our extra-foveal vision (if we foveate a blob it disappears) Receptive field –Each neuron in the visual system is responsive to only part of the entire visual field. This part is known as the cell’s receptive field

Receptive fields have both excitatory and inhibitory parts Activity in a neighbouring neuron can be decreased by activity in another neuron –Lateral inhibition Lateral inhibition heightens contrast + - A typical ganglion cell and its’ receptive field - - -

Explanation Smaller receptive fields Larger receptive fields More light on inhibitory region Excitatory centre gives a stronger response Excitatory centre gives a weaker response

Memory: Depth of processing

Craik & Tulving (1975) Depth predicts recognition List of unrelated words 3 groups each with a different decision task –1. Is the word in CAPITALS? –2. Does it rhyme with “ate"? –3. Is it a type of fish? Or does the word fit into the following sentence? Measured latency (decision time) Then surprise memory test – recognition from list of targets & distracters

Craik & Tulving’s Results As the depth/level of processing increases decisions take longer to make (latencies increase – red figures) and and Unexpected recognition improves (blue bars) RED = latencies (secs) Latencies reflect the increased processing from visual-auditory- semantic. As amount of processing increases, so did the recognition on a memory test

Visual Imagery: Propositional (Pylyshyn) / Depictive (Kosslyn) representations

Imagery = Visual perception ? Are visual images the same as visual perception? Does eidetic imagery use the same processes as perception? Do visual images contain the same properties/information as direct visual perception? –If so, then perhaps visual imagery is analogous to perception

Do visual images contain the same properties/information as direct visual perception? Image scanning studies & mental rotation studies suggest parallels between perception and imagery This hints at a deptictive/analog mechanism for mental imagery What are the differences between a depictive and an propositional explanation of visual imagery?

Propositions rely on symbols e.g. language representing relationships between objects

a) The cat is under the table b) UNDER (CAT, TABLE) Symbolic / depictive representation Propositional representation