Exteroceptive Sensory Systems

sensation

the process of detecting stimulus

perception

the higher order process of integrating, recognizing, and interpreting patterns of sensations

order of hierarchical organization of processing stimulus 

1. receptors 

2. other structures (thalamic nuclei) 

3. Cortical processing 

3 major divisions of the sensory system 

1. hierachical organization

2. functional segregation

3. parallel processing 

order of the 6 structures involved in cortical processing (from basic to complex)

1. receptors

2. thalamus

3. primary sensory cortex

4. secondary sensory cortex

5. association cortex

primary sensory cortex

lines and edges

secondary sensory cortex

shapes, colours, movement

association cortex

association with past experiences

as you move up the receptor level to the intermediate stages the 

more complex the processes get 

vision produces a

internal representation of the outside world (which is not always accurate)

perception of the world is based on

specific receptors (hardware)

vision is the

reflection of light

the higher the frequency the ____ the wave 

shorter 

the lower the frequency the ____ the wave 

longer

wavelengths of light equate to

the colour

intensity of the wavelength equates to

brightness

in the eye light travels through

the pupil 

the iris is

contractive tissue that contracts the pupil

a wide pupil is

more sensitive but less acute

light sensitivity

the ability to detect an object in dim light

acuity 

ability to see fine details of objects

binocular disparity

differences in perception b/t the 2 eyes that helps us to perceive depth

2 types of lens in the eye

1. cornea

2. lens

there is greater binocular disparity for

closer objects

ciliary muscles 

muscles in the eye that control the size and shape of the lens 

muscles that move the lens use

accommodation to focus light to the back of the eye

presbyopia

reduced ability to focus to near objects with age as lens is less flexible

the optic nerve is formed by

the axons of the retinal ganglion cells

order of cell types in the eye (front- back of eye)

retinal ganglion cells → amacrine cells → bipolar cells → horizontal cells → photoreceptors 

amacrine and horizontal cells are important for

discerning where something begins and ends

Retinal pigment epithelium

surrounds the photoreceptors and nourishes them

saccades

very quick eye movements

2 problems of the inside out retina 

1. blind spot 

   1. distortion 

Problem 1: blind spot

since the light has to track to the back of the eye there is a blind spot where the optic nerve is

solution to optic nerve blind spot

filing in the missing info through saccades

Problem 2: distortion

light passing through the cells causes distortion of the light 

solution to visual distortion 

the fovea 

fovea

space at the back of the eye with a concentration of cones and a shining of layers so light can shine right on the high acuity cones

Rods

low-light, black-and-white vision (high sensitivity but low acuity)

cones

colour vision (high acuity but low sensitivity)

rods are mostly found in the ___ of the retina

periphery 

cones are mostly found in the ___ of the retina

centre of the retina (fovea)

2 types of vision under the duplexity theory of vision

1. photopic vision

   1. scotopic vision

scotopic vision

rod mediated

many rods connected to one ganglion for easier activation

high convergence → high sensitvity+ low acuity 

photopic vision 

cone mediated 

more intense signal required to activate RGB 

low convergence → low sensitvity+ high acuity 

transduction

conversion of one from of energy into another

rhodopsin

the red photopigment in rods p

photopigment

a protein that absorbs light

Rhodopsin in the dark

1. Rhodopsin is inactive

2. Na+ channels open by cGMP

3. influx of Na+ depolarizes the cell membrane

4. rod continuously release glutamate

Rhodopsin in the light

1. cGMP is broken down

2. Na+ channels close

3. partial hyper polarization of the cell membrane

   1. glutamate release is reduced