PSY 310 EXAM 1

Dark Adaption

 process of adjusting retinal sensitivity as a person moves from a bright environment to a darker one; the reverse process is called **light adaptation**

how to measure light/dark adaption

use methods of measuring AT

perception

later steps in the perceptual process, whereby the initial sensory signals are used to “represent” objects and events so they can be identified, stored in memory, and used in thought and action

representations

information in the mind and brain used to identify objects and events, to store them in memory, and to support thought and action

distal stimulus

perceived object or event in the world

proximal stimulus

physical phenomenon evoked by a distal stimulus that impinges on the specialized cells of sense

bottom-up info

contained in neural signals from preceptors

top-down info

observer’s knowledge, expectations, and goals affect perception

neural code

a pattern of neural signals that carries info about a stimulus and can serve as a representation of that stimulus

Senses

* vision
* audition
* tactile
* olfaction
* gustation
* proprioception
* nociception
* thermoreception
* balance
* body movement

Evolution of perception

senses evolved through natural selection that bettered chanced of survival

psychophysics

explores perception by studying behavior

\-pioneered by Gustac Fechner

investigated relationship between __stimulus__ and __experience__

* investigated t__hresholds and scaling__ of perception

absolute threshold

the minimum intensity of a physical stimulus that can just be detected by an observer

Measures of Abs. Threshold: Method of Adjustment

participant observes a stimulus and adjusts a knob that directly controls the intensity of a stimulus

Measures of Abs. Threshold: Method of Constant Stimuli

participant is presented with a fixed set of stimuli covering a range of intensities that are presented repeatedly in random order, and the participant must indicate whether or not each stimulus was detected

Measures of Abs. Threshold: Staircase Method

participant is presented with a stimulus and indicated whether it was detected, based on that response, the next stimulus is either one step up or one step down in intensity

* requires less trials, more efficient

Difference Threshold (JND)

minimum difference between two stimuli that allows an observer to perceive that the 2 stimuli are different

* can use AT methods to determine JND
* not fixed

scaling

process of measuring how changes in stimulus intensity relate to changes in the perceived intensity

electrophysiology (single-cell recordings)

mostly done in animals, sometimes humans

Cognitive Neuropsychology

investigation of perceptual and cognitive deficits in order to discover how perception and cognition are carried out in the normal, undamaged brain

Modularity

human mind/brain consists of a set of distinct modules, and each carries out one or more specific function

Dissociation

damage in area X→ deficit of X but not Y

Double Dissociation

damage in area X → deficit of X in patient A; damage in area Y → deficit of Y in patient B

functional neuroimaging

fMRI, EEG, MEG, PET, DOT

study areas of brain

Light

makes vision possible

* type of electromagnetic radiation
* stream
* wave of particles
* 400-700 nm is what humans can perceive on light spectrum

Light as Particles

* photon is smallest quantity of electromagnetic radiation
* receptors (rods and cones) absorb individual particles (photons) of light
* Intensity (luminance)- number of photons reflected from a surface or emitted by a light source

3 principle fates of light entering our atmosphere

* absorption
* reflection
* refraction

optic array

what you can see

* spatial pattern of light rays varying in brightness and color entering your eyes from different locations in the scene
* constantly changing as objects move and observer moves in relation to objects

brightness

the “perceived” intensity of the light, number of photons

color

wavelength

field of view

portion of surrounding space you can see with your eyes in a given position in their sockets

Lens (know location)

further refracts light, can adjust the amount of refraction by altering its thickness

* focuses light on the retina

what factors can change the optic array over time?

eye movement, motion of observer, lighting conditions, motion of objects

Pupil

hole that lets light into the eye

Cornea (know location)

refracts light through the pupil

Iris

controls the dilation of the pupil and thus the amount of light let into the eye

optic axis

forms diameter line from front to back and passes through the lens’ center

optical disc (blind spot)

location on the retina where the axons of the RGCs exit the eye; contains no photoreceptors; (know location)

sensation

 initial steps in the perceptual process, whereby physical features of the environment are converted into electrochemical signals that are sent to the brain for processing

retina (know location)

inner membrane of the eye

* complex structure with many cell types
* Pattern of light on the retina is an inverted two-dimensional “retinal image” of the current field of view

Fovea (know location)

region in the center of the retina where the light from objects at the center of our gaze strikes the retina

* contains no rods and a very high density of cones

Accomodation

adjustment of the shape of a lens so light from objects at different distances focuses correctly on the retina

* Weak lens don’t refract light much- far away
* Strong lens refracts light sharply-close up

rods

provide black and white vision in dim lighting

cones

provide high-acuity color vision in bright light

What is the goal of the optic system

form a clear image on the retina

optic nerve (know location)

nerve formed by the bundling together of axons at the RGCs; ot exits the eye through the optic disc (blind spot)

3 main layers of the Retina

* ganglion cell layer, inner nuclear layer, and outer nuclear layer

outer layer of retina

nucleus part of the photoreceptors (rods and cones)

* At fovea, the ganglion cell layer and inner nuclear layer are pushed to the side to minimize interference with the image at the fovea by giving incoming light more direct access to photoreceptors
* No rods at fovea

Why are there 20x more rods than cones

reflects their different functions

* need more rods to see in low brightness settings

transduction of light

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* Occurs when a photon of light is absorbed by a photopigment and changes in shape, i.e, __photoisomerization__


* 11-cis retinal is converted by light into all-trans retinal
* __**purpose is to turn light into neural signals**__

photopigment regeneration

 transforming the all-trans isomer back to the 11-cis isomer

* Process by which light is transduced to a neural signal is “cyclical”

Retinal Ganglion Cells

circuits in the retina send info to the brain

Convergence

property of retinal circuits in which multiple photoreceptors send signals to one RGC

High Convergence

many-to-one, maximizing sensitivity (rods)

No Convergence

ono-to-one, maximizing acuity (cones

Why does high convergence maximize sensitivity

__***spatial summation***__-signals from photoreceptors in some small space on the retina add up to affect the response of the RGC

* firing rate of RGC increases as the number of photoreceptors that are activated by light increases

Why does no convergence maximize acuity

spatial resolution is better because it provides info about the location of light because the ratio is 1:1

receptive fields

region of sensory surface that cause a change in the firing rate of a neuron that “monitors” that region of the surface

* vary in size; areas in the fovea are smaller than the periphery

Midget ganglion

smaller RF

Parasol ganglion

larger RF

center-surround RF

RGCs have center-surround RFs

* center of RF responds different to stimulation than the surrounding portion fo the field

On-center RF

RGCs increase firing rate when more light hits the center relative to the surround

off-center RF

RGC’s increase firing rate when more light hits surround relative to center

preferred stimulus

type of stimulus that produces a neuron’s max. firing rate

our eyes can sees some of the electromagnetic radiation in the environment ___

visible light (400-700 nm)

the pattern of light entering out eyes is called the___

optic array

the task of the eyes is to transform the pattern of light into___carrying this info to the brain

neural signals

Pathway of light

light→rods and cones→bipolar cells→ RGCs

lateral inhibition

* center surround RGSc exhibit this
* Refers to the inhibitory signals sent by __**horizontal cells**__, which modify the responses of photoreceptors and provide a way in which neural activity in one part of the circuit can influence neural activity in adjacent parts of the circuit

why is lateral inhibition useful

edge enhancement- process by which the visual system makes edges as visible as possible, facilitating perception of where one object or surfaces ends in the retinal image and another begins

* detecting boundaries in dim light
* sharpens bondaries

what is responsible for edge enhancement

RGCs with center-surround RFs

cataracts

progressive clouding of the lens; can lead to blindness of left untreated

LASIK

surgery to reshape the cornea to correct disorders of accommodation

focal length

* strong lens=shorter focal length (closer objects)
* weak lens=longer focal length (further away objects

From eye to brain

neural signals from the retina travel along increasingly complex networks as they go deeper into the brain

functional specialization

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specialization of diff. neural pathways and different areas of the brain for representing diff. kinds of info

retinotopic mapping

an arrangement of neurons in the visual system whereby signals from RGCs with receptive fields that are next to each other on the retina travel to neurons that are next to each other in each visual area of the brain

optic nerve

formed by axons of RGC

optic chiasm

where left and right optic nerve intersect

lateral geniculate nucleus

* 90% of axons in the optic tract go here
* sends signals to the __**primary visual cortex (V1)**__ via the __**optic radiations**__

superior colliculus

where other 10% of axons go

contralateral representation of visual space

visual info from right visual field is represented in the left hemisphere on the brain and vice versa

6 layers if LGN

layer 1 and 2- magnocellular layers: large cell bodies important for movement and change detection

layer 3-6-parvocellular layers: small cell bodies important for discrimination of color, shape, texture, and depth

* thinner layers between- konicellular layers (very small cell bodies)

from retina to LGN

left visual field→ right LGN

right visual field→ left LGN

* each LGN receives signals from both eyes, but each LGN layer receives signals from only one eye

Right Eye

Right LGN 2,3,5 (ipsilateral eye)

Left Eye

right LGN 1,4,6 (contralateral eye)

Left LGN

receives info from both eyes and right field

LGN and attention

* receives inputs from retina, V1 and other cortical regions (top-down info)
* engages differently when looking out of the corner of the eye vs. center
* not just a relay center

superior colliculus

* form tectum (roof) of midbrain together with the inferior colliculi
* helps control eye movements of visual stimuli
* some layers receive info from non-visual areas; thought to be site of multi sensory integration where signals of different systems combined

Primary visual cortex (v1)

* in occipital lobe
* first cortical area to receive visual info
* highly organized (ocular dominance columns, orientation columns, organized retinotopically)
* simple, complex, and end-stopped cells

response property of V1 neurons

* most effectively stimulated by bars/edges with narrow ranges of orientations (vertical orientation)

orientation tuning curve

avg. response of an orientation-tuned neuron such as a simple cell to stimuli with different orientations

population code

A consistent difference in the patterning of the relative responses of a pop. of __differently turned neurons__; used to compute perceptual features such as the orientation of a visual stimulus

complex cells

* second main category of cells in V1 (most numerous)
* also tuned for orientation
* They respond as well to a light bar on a dark background as to a dark bar on a light background
* Respond equally well to a bar at almost any location within their RF

Simple cells

when bar of light is tilted across RF (off-center) they tend to respond less strongly because the light is stimulating fewer of the excitatory centers and more of the inhibitory surrounds

organization of V1

* characterized by columns that run vertically through layers
* cortical column-functional building block of cortex

ocular dominance column

neurons that receive signals mainly from one eye

* Cells in the center of each ODC are monocular whereas cells in a border zone between columns are binocular (**important for depth perception**); tell brain which eye info is coming from

orientation columns

neurons within the same column have the same (or very similar) orientation tuning

retinotopic maps

 neurons from the same column have RFs located in the same area of the retina

* Neurons in adjacent columns have RFs in adjacent areas
* allows someone looking at brain activity can infer what you are looking at