PSYC111 module 2 (sensation & perception)

Sensation, perception

• registering of sensory info by the brain

• assignment of meaning to that sensory info

Are sensation and perception the same or different processes?

They all do sensation and perception. Early on in the visual system there is more sensation but there is still a little bit of perception.

As you get to the end of the visual system there is more perception and less sensation

How is sensory info implemented neurally?

• Sensory organs absorb energy

• Energy is transduced into neural signal

• neural signal sent throughout the brain for further processing

Wavelength, Amplitude

• Colour that you see

• How bright you see the colour

Outer layer of eye

Cornea

• Transparent, focuses image on retina

Middle layer of eye

Choroid (vascular tunic)

• eye’s blood supply, provides nutrients to keep tissue alive and discards waste

• doesn’t cover the whole eye

• Fluid is in the anterior and posterior chambers which reaches cornea and lens

Inner layer of eye, cataracts

• Iris= can extend and contract them, this changes the size of your pupil

• Pupil= becomes bigger or smaller to let more or less light in

• Lens= behind pupil, attached to muscles that pull or push the lens to focus eyes near or far (accommodation)

Cataracts

• condition that makes lens cloudy, can make you blind

• taking cataracts out will allow them to see again.

• If you are born with it and don't take the lens out before the critical visual period of development you still won't be able to see.

retina

• Surrounds the eye

• Contains photoreceptors (rods & cones) that convert electromagnetic energy into neural signal

Rods vs cones

Perform transduction (electromagnetic energy → neural signal)

• 120 mil, no colour, active at night, high resolution, peripheral

• 7 mil, colour, active during daytime, low resolution, almost all are in fovea, central

blindspot, Optic nerve, Bipolar cells & retinal ganglion cells

• has no photoreceptors, where the axons of the ganglion cells exit the eye

• axons of ganglion cells, size of pencil

• engage in processing visual image

Central sulcus, lateral sulcus, Pareto-occipital sulcus

cortex,sub cortex and lobes of the brain

• convolutions, layer below convolutions

• Occipital lobe= ONLY visual functions

• Temporal= auditory, visual and memory

• Parietal= spatial processing, damage to right parietal= ignore left side

• Frontal= executive functions, motor, organizing behavior, integrates info, sends motor info to motor cortex

Visual pathways

1. Eyes→ subcortex. Eyes to lateral geneculate nucleus (LGN). Nasal fibres cross over, temporal don’t.

2. Subcortex→ cortex. LGN to primary visual cortex (V1) in occipital lobe.

3. Cortical visual pathways beyond V1

Mishkin & Ungerleider 1982. Monkeys trained on object discrimination task and landmark discrimination test.

• Visual discrimination task= one object will have a reward when you pick it up. See if they go back to the one with the reward in the next trials even when position of objects change

• Landmark discrimination task= reward is hidden under an object but both objects look the same. The object closest to the cylinder is the one with the reward.

  After learning both tasks half got parietal lesions and half temporal lesions

• temporal lobe important for object discrimination, parietal lobe for landmark discrimination

Mishkin & Ungerleider 1982. Beyond V1

Beyond V1 info travels along dorsal and ventral streams

• Dorsal= goes into parietal lobe, Important for position (where) of objects, spatial vision

• Ventral= goes into temporal lobe, important for (where) of objects, pattern vision

neural properties along visual system

• Electrophysiology studies= wires in brain to see AP of neurons

• From eyes up to V1= Rods and cones (change in illumination), retinal ganglion cells and LGN cells create spots of light, V1 cells like lines more than spots of light.

• Beyond V1 (in ventral visual stream)= Inferior temporal (IT) cortex. Grandmother cells respond to certain shapes (feature detectors)

• Retinotopic mapping= Point-to-point mapping of external world onto a brain area. V1 and before. V1 is in the back of occipital lobe. After V1 no retinotopic mapping.

Visual system

• As you go higher into visual system (away from eyes) info becomes more complex

• features that drive a cell change, from basic illumination levels (rods & cones) to spots of light (RG cells, LGN cells) to lines (V1) to complex features (IT cortex cells).

• Where info has to be changes from small specific areas (V1 cells) to large space (IT cells)

Lateral inhibition

• They look like different shades even though both squares are 20 units and are the same colour. Cells are inhibiting the neighboring colour.

• Retinal ganglion cells like dots

• Centre surround architecture increases contrast and brightenss contrast

Herman grid illusion

• arises from centre surround architecture of RGCs

• when bathed in diffuse light or darkness the brain sends nothing bc the numbers cancel out

• When presented with dark or light dot the RGC sends maximum signal

Damage at:

• Right optic nerve= right monocular blindness

• Optic chiasm= bitemporal hemianopia

• Right optic tract= Left homonymous hemianopia

• Right V1= Left homonymous hemianopia with macular sparing (dot in middle)

Patient DB, blindsight

removal of tumour in right occipital lobe

• Left homonymous hemianopia

• Can’t identify static or moving object (bc info bypassing V1) but can localise it in space (info reaching dorsal/where path)

• Sensing moving object= info reaching V5

Achromatopsia, Akinetopsia

• Absence of colour vision, damage to V4, can result from missing cones, colour blindness

• Absence of motion vision, damage to V5, can see that something is moving but can’t see the object

Visual agnosias

Inability to name object even though you can see it well. All have preserved colour and motion perception.

• apperceptive= Bilateral damage to V1, peppery mask, failure of object recognition, poor matching & copying.

• Dorsal simultagnosia= bilateral damage to parietal lobes, failure of object recognition bc spatial perceptual impairment, can recognise objects but not more than one at a time, can’t see all objects at the same time

• ventral simultagnosia= damage to ventral stream beyond V4, failure of object recognition bc complex perceptual impairment, can see multiple objects but not clearly

• Associative= Damage to higher order (than V5). copying of images is normal but slavish (struggling). Fail incomplete figures test quicker.

Top-down vs bottom-up theories, interactive theories of pattern perception

• context dependent, hypothesis testing, knowledge and experience,

• Detail dependent, building on small features until details emerge, sensory info, Evidence= errors & confusion.

• theories that accomodate both

binocular cues

• Retinal disparity= 2 images at different depths will result in diff image distances on the retina, brain interprets it as depth

• Convergence & divergence= near objects make eyes converge, far objects cause eyes to diverge, brain interprets it as depth

Monocular cues

• Interposition= Object covering another object is closer than the one that is being covered

• Relative size= people smaller in the picture are further away but irl they are the same size

• Linear perspective

• Heightened plane= not very powerful clue, objects

• Texture gradient

• Light and shadow

Young Hemlotz trichromatic theory

• 3 cones in the retina and each are maximally sensitive to a certain colour

•  cones sensitive to blue, some to green and some to red (short, medium and long wavelengths)

• doesn’t account for why colour blindness is in pairs and why we get colour after effects

Opponent process theory

Bipolar RGCs are opponent process cells

• Short wavelength= blue/yellow opponent cells

• Medium wavelength= red/green opponent cells

• Long wavelengths= black/white opponent cells

1. Renes Descartes early 1600s

• brain symmetrical

• thought that there was a structure that unites everything and is between the two hemispheres (pineal gland)

• WRONG

2. Gal &Spurzheim early 1800s

• Phrenology= Bumps associated with skills, dents associated with under-developed behaviors.

• Faculties= odd behaviors mapped onto the brain

• Problems= No actual correlations between bumps and depression on the outside of the skull and the brain.

3. Paul Broca 1861

• Only thing Tan could say is "tan"= language impairment. Comprehension is fine but motor impairment.

• Tan had big lesion in the left frontal lobe. This is the brocas area.

• Language is localised in the left frontal lobe

• brocas aphasia= difficulty with language output

3. Karl Wernicke 1873

• Language problem in patient, output is normal but comprehension impaired.

• Lesion in left temporal lobe

4. Fritsch and Hitizig 1870

• motor cortex caused contralateral (opposite) movement of body parts

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  Stimulating thumb movements on the right side causes movement of the left thumb.

Damage to occipital lobe

• Blindness & blindness

• Apperceptive agnosia

Temporal lobe parts, damage

• Lateral surface= superior, middle, inferior temporal gyrus

• Medial surface= medial temporal lobe

  Superior temporal damage (auditory)

• deafness

• Wernickes aphasia

• Auditory agnosia

  Middle & inferior temporal damage

• Achromatopsia, Akinetopsia

• Ventral simultagnosia

• Associative agnosia

  medial temporal lobe

• Left= Hearing okay, verbal memory impaired

• Right= Copying okay, visual memory impaired

Patient HM

Removed medial temporal lobe= old memories still there but new memories not saved as much

• retrograde amnesia

• Anterograde amnesia

Mirror-drawing task, tower of Hanoi

• ppl with medial temporal lobe damage do have some spared memory. Draw outline of star and then trace by using reflection in mirror. First time you are bad at it, memory helps you improve as you do it more times

Multiple memory systems

Declarative= affected by medial temp lobe impairment

 Nondeclarative= not affected by MTL impairment, improve over many trials

• e.g. riding a bike, mirror drawing task

• Person that has MTL impairment won't remember doing it 10mins later but if given the task again they can do it

Left parietal lobe damage

• Agraphia= Difficulty in writing, difficulty in organising information on the page

• Acalculia= Difficulty in mathematics, because impairment in organizing information, don’t know where to put the numbers

• Right/left confusion

• Dyslexia

• Difficulty drawing (details)

Right parietal lobe damage

• difficulty recognising unfamiliar view of object

• Difficulty drawing (overall shape)

• Contralateral neglect= Only sees one side. Instead of turning to the left she swings whole body around until stuff comes into view.

tests for contralateral neglect

right parietal lobe damage

• Line or letter cancellation

• Line bisection= Middle part of the right half of the line instead of the middle of the whole line

• Neglect is a post-perceptual problem bc both right and left are processed but only one side is seen (burning house and Milan pizza experiments)

Ego centred vs Object centred neglect

• ignore entire left half but not right. Draws the girl but not the boy

• doesn’t matter where in the visual field the object is the left half of the object is ignored. Draws the right half of the girl and right half of the boy

What is being neglected? Driver, Baylis, Goodrich & Rafael 1994

Ppl with contralateral neglect= Saw the gap in the left half but not in the right half because of ego

• It looks like object based neglect but its actually ego because there is an axis that reinstates ego based neglect

Damage to the right parietal lobe neglect the left, have to be right handed

Damage to the left parietal lobe neglect the right if they are left handed

Frontal lobe

• Motor cortex

• Premotor cortex (damage= brocas aphasia)

• Prefrontal cortex

• Orbitofrontal cortex

Loss of divergent thinking

Frontal lobe damage (prefrontal cortex)

• Word fluency test= "how many words can you write that start with the letter S". Impairment to prefrontal cortex would cause you to think of less words, can't generate as many words. "how many words can you write starting with C but only 4 letters long". Rule breaking, ignore the instruction.

• Design fluency test= Low output or high output with the same figure over and over again

  

Impairment to frontal lobe

• Brocas aphasia

• Loss of divergent thinking

• Impairments with response inhibition

• Stroop interference test= read colour not word

• Environmental dependency syndrome (exaggerated imitation of others or using things infront of them)

• Change in personality

Wisconsin card sorting test

tests for response inhibition for frontal lobe damage

• "pick up a card from the deck and match it with one of the 4 cards"

  Will be told whether it is correct or incorrect. Not clear which one to match it to.

• By the third trial you should be able to figure out the pattern. When getting 10 right in a row it is now incorrect but should be able to figure out the new rule

• Person with impairment in pre frontal cortex will take a lot more trials to figure it out