Perception part 1 (lec. 4) Flashcards
Color perception influence on judgment
Color can impact how we perceive and evaluate things. Some people think black dogs are not
as friendly as other colored dogs.
A study found that people rated photos of black dogs as lower in Agreeableness, Conscientiousness, and Emotional Stability than golden dogs. Perhaps this is why black dogs are passed over for adoption in favor of lighter-colored animals.
From sensation to perception
Stimulus energy -> sensory receptors -> neural impulses -> brain. The closer to the brain, the closer the experience is to a perception (just stimulus: sensation)
Exteroceptive sensations
Any form of sensation that results from stimuli located outside the body detected by sensory organs. Vision (light entering eye), audition (air vibrations entering ear canal), touch (pressure, heat, vibrations on skin), taste (chemicals in mouth), smell (airborne chemicals in nose)
Interoceptive sensations
Sensations from inside our body
* Proprioception: Sense of where our limbs are in space
* Nociception: Sense of pain due to body damage
* Equilibrioception: Sense of balance
Dancers have increased interoceptive accuracy: they could estimate heart rate more accurately
than non-dancers (this was unrelated to fitness levels or counting ability)
Synaesthesia
A neurological condition in which one sense automatically triggers the experience of another sense: hear colours, smell sounds, see time… It has a genetic component, and is more common in women. Specific pairings tend to be stable over the lifetime of the individual. Artists are 8x more likely to have synesthesia than non-artists, ex. Billie Eilish, Van Gogh…
Forms of synesthesia
- Grapheme-colour synesthesia: Colour with letter/numbers, ex. “7 is pale blue with a pleasant, soft, nice personality”
- Chromesthesia: Sound can evoke an experience of colour
Why synaesthesia is important in studying perception
- It represents the importance of individual differences (ex. how Joe with chromesthesia experiences the visual world likely ”sounds” different than how Barb experiences the visual world)
- It encourages a view that brains are organized as “talking” circuits. It is explained as cross-talk between processing regions for different senses. Ex. fMRI studies show activating of V4 color processing region during words for grapheme–colour synaesthetes
McGurk effect
-When you hear what you see. It is a multisensory illusion:
- A voice articulating a consonant (/ba/) paired with a face articulating another one (/fa/) leads you to “hear” what you “see”.
- A change in auditory perception from visual perception to reconcile these incongruent inputs
It illustrates integration of and cross-talk among senses, with a similar message as synaesthesia. It also illustrates the dominance of visual input.
The visual system, early vs. late
Early visual processing :
* Sensation
* Eyes and the optic nerve
Late visual processing
* Perception
* The visual cortex or
occipital lobe
Steps of visual processing
- Light waves enter the eye, and then projected onto the retina. The retina forms an inverted image (later processes turn this image around)
- Retina photoreceptors convert light to electrical activity
* Rods: low light levels for night vision
* Cones: high light levels for detailed color vision - The electrical signal is sent to bipolar cells, then sent on to the ganglion cells
- The signal exits through the optic nerve, to the brain for later visual processing
Information compression
- Millions of photoreceptors in each retina converge onto 100x fewer ganglion cells -> optic nerve -> brain
- Input from the eyes to the brain is compressed
- You don’t ‘see’ everything that is out there in the world
Photoreceptor distribution
- Cones are concentrated in the
fovea (small area on the the central part of the visual field). Thus, the center of your visual field is most detailed - Rods are mostly in the periphery. Thus, periphery of your visual field is less detailed and less accurate.
Blindspot
- Photoreceptors are at the back of the retina (farther from the ‘world’); Ganglion cells are at the front
- Ganglion cells make up the optic nerve that exits to the brain. They must pass through the photoreceptor layer. At this ‘exit location’, there are no photoreceptors (and so no vision)
- We don’t actually “see” our blindspot: there is perceptual filling-in (later visual processes in the brain provide the missing information by ‘interpolating’ visual information (ex. colors) from surrounding areas. The left and right visual fields can compensate for each other’s blindspot.
How to “see” your blindspot
- Close your left eye. Keep it closed.
- Hold your left thumb at arms length and look at it with your right eye.
- Hold up you right thumb next to your left thumb.
- Continue looking only at your left thumb while slowly moving your right thumb to the right.
- Your right thumb will disappear when your thumbs are separated by about 6 inches.
- Remember the whole time to fixate your left thumb with your right eye.
- Once you have found your blind spot, move your right thumb around to see how big it is.
From early to late visual processing pathway
- The thalamus (lateral geniculate nucleus, LGN) is the way-station
- The optic nerve of each eye transmits information to both hemispheres
- Contralateral representation: left visual field is perceived via the right hemisphere, and vice versa.
