PS1102 - Introduction to sensation, perception and cognition

Phonton

• single particle of light

• light travels in waves as electromagnetic radiation

Amplitude

• the intensity of light

wavelength

• the distance between the peaks of the waves

Frequency

• the number of waves that pass a specific point every second

what is the range of visible light spectrum for humans

• humans can see electromagnetic radiation with wavelengths between 380-760mm

function of the cornea

• the transparent outer coating at the front of the eye

• principal means of focus

function of the sclera

• white opaque outer coating of the eye

Pupil

the circular hole in the center of the iris where light enters the eye

Iris

the pigmented part of the eye visible through the cornea

Anterior chamber

between the cornea and iris - contains aqueous

Posterior chamber

between the iris and lens - contains aqueous

Vitreous chamber

behind the lens - contains vitreous

Accomodation

• process where the lens changes shape to adjust the eye’s focus for objects at different distances

Phototransduction

• the process occuring in the retina where light energy (phontons) is transformed into electrochemical energy

path of light through the eye to the brain

light - cornea - pupil - lens - retina - optic nerve

Rods

• -120 million

• responsible for vision at low light levels

• very sensitive to darkness - coarse spatial structure

Cones

• - 6 million

• responsible for bright light and colour vision

Fovea

• contains only cones - this is where the center of an image falls

Peripheral retina

• contains both rods and cones

blind spot

• the point in the retina where the optic nerve leaves the eye to go to the brain

• contains no photoreceptors

why do we not notice our blind spot

• as it is located in our peripheral visual field and the brain uses a process called filling in to complete the image

the role of the retinal ganglion cells

• they summarise input from a population of photoreceptors

• their axons form the optic nerve and carry signals out of the eye to the brain

Physiological Module

• a brain structure containing a high proportion of neurons that respond selectively to a specific quality or type of information

• These are defined by the information they process and their precise localisation in the brain

middle temporal (MT) area

• a specialised module for visual movement

• around 90% of its neurons respond only to movement in specific directions

• damage here severely impairs the ability to perceive motion

main visual pathway

• photoreceptors ( rods and cones) in the retina

• retinal ganglion cells

• optic nerve (made of ganglion cell axons)

• lateral geniculate nucleus

• visual cortex

retinotopically mapped

• every level of the visual system (like the LGN and cortex) is organised so that each location corresponds to a specific spot of the retina

• neighbouring areas on retina remain neighbours in the brains map

Cortical magnification factor

• the brain devotes more cortical area to the central part of the visual field (the fovea) than to the edges (periphery)

• This allows us to see details much better in our central vision compared to our peripheral vision

subcortical pathways

• not all visual info goes to the cortex

• spme goes to areas like the superior colliculus

Blindsight

• occurs when patients with damage to the visual cortex can still accurately respond to visual stimuli despite having no conscious visual experience of them

ventral stream

• the “what” pathway

• used for perception and recognition

dorsal stream

• the “how” pathway

• used for action

double dissociation

• it proves that two functions (like perception and action) involve different mechanisms that work independently

• This is shown by comparing patients with different types of brain damage

What happens in the case of DF

• damage to the ventral pathway meant DF could not recognise objects or shapes visually

• However her Dorsal pathway was fine so she could still perform actions like posting a card through a slot even though she couldn’t describe the slots orientation

Optic ataxia

• the opposite of DF’s condition - caused by dorsal pathway damage

• These patients have normal recognition but struggle with vision-guided actions such as making errors when trying to reach through an orientated slot

Massive modularity

• the mind is like a Swiss Army knife a collection of specialised tools evolved to solve specific problems

Massive redeployment

More recently evolved functions are distributed over wider regions of the brain rather than single modules

How does cognitive science define a module

• modules are seen as hypothetical/functional rather than just physical locations

• According to coltheart the most critical feature is domain specificity - responding only to a specific class of stimuli

Fodor’s modular characteristics

• modules tend to be - domain specific innately specified, informationally encapsulated ( they only see what they need to) fast, hard wired and autonomous

Psychophysics

• the study of the relationship between the physical stimuli and the perceptual experiences they generate

Two main assumptions of psychophysics

• there is a threshold below which no sensation is present

• There is an orderly relationship between the intensity of a stimulus and the level of sensation it produces

Forced choice method in psychophysics

• a task where participants choose between specific options such as whether a stimulus is present or absent or if it is moving left or right

Saccades

• accurate, high velocity eye movements used to move the fovea to areas of interest

Fixations

• periods when the eye is relatively still to take in information

Small eye movements that occur during fixation

• Tremor

• Drift - slow movements

• Micro saccades - fast jerk like movements

Core idea of active vision

• we explore the world by collecting a series of snapshots during fixations and integrating them to create the illusion of a continuous detailed scene even tough our high acuity vision is limited to a small area

What happens to visual information during a saccade

• visual information is suppressed during eye movements to prevent a blurred image as the eye moves

compare the Fovea, Parafovea and Periphery

• the fovea (0-2°) has the greatest visual acuity and highest density of photoreceptors - the Parafovea (2-4°) and Periphery 4+°) have significantly lower resolution

what is Posner’s pre-curing paradigm

• a study where participants fixate on a central spot and react to targets - valid trials (80%) cue on the correct location, while invalid trials (20%) cue the wrong one results show faster reaction times for validly cued locations supporting the spatial spotlight analogy of attention

difference between central and peripheral cues

• central cues (like and arrow) cause an voluntary shift of attention peripheral cues cause an automatic shift

what are the benefits of covert attention

• covert attention shifts are often linked to planning of eye movements, sequential scanning without moving the eyes is slow and difficult because the two systems are connected

what are the four types of eye movements in coordinated action

• locate - find the object to be used

• direct - fixate on the object to be manipulated

• guide - bring two objects together

• check - monitor the state of the object

where do drivers look when steering around a corner

• they fixate on the tangent point on the inside of the curve to help their path

how do we define colour

• colour is what lets us tell two surfaces apart even if they have the exact same level of brightness

• this is known as isoluminant

what are the three ways we experience colour

• physically colour is made of wavelength and intensity

• different wavelengths of light correspond to different colours we see

what are the two main functions of colour perception

• it used for signalling (like knowing if a banana is ripe) and detection (like finding cherries among green leaves)

what wavelengths can humans see

• we see the visible spectrum which ranges from 400 to 700 nanometers

• Blue is a short wavelength (450-490nm), green is medium (500-575nm), and red is long (620-700nm

how do we see white, black and objects

• white is a mix of all wavelengths while black is the absence of light

• we see objects because they reflect light ; a reflectance curve shows which wavelength an object reflects

What is the difference between chromatic and achromatic light?

• chromatic light happens when some wavelengths are reflected more than other

• achromatic light (like white or grey) is spread across the whole spectrum

what is the difference between mixing light and mixing paint

• additive mixing (mixing lights) adds wavelengths together

• subtractive mixing (mixing paints) subtracts wavelengths because more light is absorbed

What is the Trichromatic Theory of colour vision

• this theory says our colour vision is based on three types of cone receptors in the retina

• these cones are sensitive to different wavelengths : short, medium and long

where are cones found in the eye

• cones are mostly packed into the fovea (the centre of the retina)

• because there are fewer cones on the edges of our vision we are much worse at seeing colour in our periphery

what is the opponent-process theory

• this theory suggests we process colour in opposite pairs

• special ganglion cells in the retina group cone activity into codes such as a Blue+/Yellow- channel where blue enhances the signal and yellow inhibits it

what are the main opponent colour pairs

• the pairs are Red vs Green, Blue vs Yellow and Black vs White (the achromatic axis)

• yellow is actually seen as a combination of Red and Green receptor activity

What are Protanopia and Deuteranopia?

• A Protanope is missing the "long" (red) wavelength cones

• A Deuteranope is missing the "medium" (green) wavelength cones

What is a Tritanope and how is colour blindness tested

• A Tritanope is missing "short" (blue) wavelength cones.

• Doctors use the Ishihara Test (plates with dots and numbers) to detect these deficiencies

What is Colour Constancy

• this is our ability to see an object as the same colour even when the lighting changes (like moving from bright sunlight to a yellow indoor bulb). -

• Our brain estimates the object's true reflectance regardless of the light source