Chap 3 - PSYC 213 Book Notes Chapter 3 Synaesthesia...

PSYC 213 Book Notes
Chapter 3
Synaesthesia: confusing the senses
- Mixing of senses in the brain
 Stimulation of one sense simultaneously produces another sensation in a
different modality
- Different forms
 Ex : grapheme-color synaesthesia : seeing certain numbers or letters as
certain colors
- Can you learn to be a synesthe?
Experiment: Colizoli 2016:
 16 non-synesthete participants
 task: read books with certain letters printed in certain colors (> 1000 000
words)
 results: subjectively reported ‘synaesthesia’: ‘i am experiencing color
when thinking about certain letters”
 problems with this study: no control group!
A common misunderstanding
- when we see, there is input into the eye
- extramission belief: when we see,t here is a ray that exits the eye onto an object
(an output; false)
The Visual System
 Early visual processing: Sensation  Eyes and the optic nerve
1. Light waves inter the eye, focused onto the retina (a thin layer of tissue at
back of eye)
2. Photoreceptors in the retina convert light to electrical activity
 Rods: low light level; night vision
 Cones: high light level; detail
3. The electrical signal is sent to bipolar cells and then to ganglion cells
4. Signal exits through the optic nerve to the brain
- Info is compressed: millions of photoreceptors in each retina converge into 100x
fewer ganglion cells  optic nerve  brain
- Cells are non-uniformly distributed
 Most cones are in fovea (small area in centre of visual field)  so more
detailed vision here
 More rods on outside of fovea  peripheral vision is less detailed
 bottom line: perception is contructive + perceiving is not just seeing

 Early to later visual processing
- Optic nerve
- Each eye’s optic nerve transmits info to both hem
 Left visual field perceived via right hem and vice versa
 contralaterality: opposite site
 Later visual processing: Perception  Visual cortex (occipital lobe)
- Primary Visual Cortex: specialized regions of cells that process particular visual
attributes or features
 Edges, angles, color, light, size, motion, dimensions
- Visual Association Area: interprets info acquired through PVC  assigns meaning
to what we see
- Processing streams: the what (ventrla) and where (dorsal) pathways
- Neuroimaging studies: object identification VS spatial location tasks activate the
what and where pathways
Lessons from the visual system
- We don’t sense or perceive info directly
- Visual stimuli is latered/ ‘broken apart’ in the processing pipeline (compression +
functional specialization in PVC)
- These pieces of info are integrated back together to be interpreted as a whole
 perceiveing = constructing
Visual agnosia: an inability to identify objects visually even though they can be
identified using other senses (ex: touch)
 Basic sensory systems are intact, not blindess
 Visual association areas are damaged
- Dissociation between being able to see visual features and interpreting those visual
features
 problems assigning meaning
- Can be selective to particular types of processing
 there are cases of selective deficits in visual recognition
Propospagnosia