Sensation

the process by which organs gather info about the environment and transmit it to the brain for initial processing

Perception

The brain selects, organises and interprets sensations

Name the key anatomy of the eye

Cornea - tough transparent tissue covering the eye to protect from damage. Light passes through a small area of clear fluid. Equus humor - clear fluid where light passes through Pupil iris - muscles contract or expand (dilate or constrict) to control the amount of light entering the eye. lens - light is focused here into the retina retina - contains necessary receptors to transmute light into neural impulses subsection of retina are rods and cones

FOVEA

the middle of the retina about 1-2 degree of visual angle in size mostly cones densely packed photoreceptors area of clear vision Used to read!

Cones

less sensitive - needs strong light centre of retina - fovea detailed vision responds to wavelength (colour) Three different types: BLUE (shortwave), GREEN (middle), RED (longwavelength)

Rods

sensitive good for dim lighting cannot distinguish colour in periphery

Explain signal detection theory

How we come to decide when there is only two decisions to make (yes/no).

What are the four possibilities of signal detection theory, and what do they each mean?

Hit Correct ‘yes’ to a ‘yes’ item Miss Identify ‘no’ to a ‘yes’ item Correct rejection Identify ‘no’ to a ‘no’ item False Alarm Identify ‘yes’ to a ‘no’ item

What does the pupil do

Dilates and contracts to: - changes in ambient lighting - emotion, motivation, arousal

What does the retina do

contains two types of cells that transduce light, generating electrical signals when struck by light waves. Contains rods and cones.

What are the three broad principles of sensation and perception?

1. What we see does not perfectly match up with what is in front of us - measuring this is the realm of psychophysics. 2. Sensation and perception are active processes - we actively construct and organise our experiences 3. Sensation and perception are ADAPTIVE - a result of survival and reproduction - evolution

What are the common features to all sensory systems?

A) They each have sensory receptors that: 1. detect physical energy (light or sound waves) 2. translate physical simulation into neural signals (transduction) B) each requires a min. amount of energy (threshold) to activate the system C) requires constant decision making - seperating meaningless info from important info D) requires ability to detect changes in simulation E) effiecient sensory processing requires 'turning down the volume' or repressing redundant information.

Absolute threshold

the minimum amount of stimulus energy that must be present for a stimulus to be detected 50% of the time. Can vary from person to person or situation

How can thresholds be affected?

External noise - aircon, sitting on a chair, etc. internal noise - motivation, fatigue levels, etc. - random firing of neurons

What is a JND?

Just noticeable difference the lowest level of simulation to sense a change in simulation has occurred

What is weber's law on JND?

Regardless of the magnitude if two stimuli, the second must differ by a constant proportion from the first to be percieved as different

Weber fraction

the ratio of change in intensity required to produce a JND

What is fechner's law?

the magnitude of a stimulus grows geometrically as the subjective experience of intensity grows arithmetically.

What is steven's power law?

As percieved intensity of the stimulus grows arithmetically, the actual magnitude of the stimulus grows exponentially (squared, cubed, etc.)

transduction

the process of converting physical energy pr stimulus information into neural impulses

LIGHT

a form of electromagnetic energy that moves in waves wavelength - the distance between one peak to another (determines colour) ampiltude - height of a wave determine pyschological experience of brightness visible spectrum: 400 - 750 nanometers (nm)

what is the visible spectrum?

the light and colour the human eye can see about 400-750 nanometers (nm)

What do wavelengths tell us ?

the distance from one peak to another - shows us colour and spectrums

What does amplitude show us?

The height of a wave - shows us how we experience brightness pyschologically

Retina layout - please describe

At the very back - photoreceptors: They transduce light into neural signals. There are two types of these - rods and cones middle - Front - optnic nerve recieves the signal and sends it through the brain.

What is the Trichromatic theory?

Developed by young and Helmholtz: colour is explained by differential activation of three colour receptors in the eye.

What are some phenomena that trichromacy theory cannot explain?

Seeing after images - specifically different colours to the ones that were shown.

What is the opponent process theory?

colours are derived from activity of three antagonistic systems: Black-white, red-green, blue-yellow). Once an activated cell is fatigues (overstimulated - you stare at one colour too long), you see the opposite colour

Which colour theory best describes the processes in the retina?

trichromatic theory - the three types of cones.

What colour theory best describes visual processing in the brain?

opponent-process theory

What are bottom up factors?

based on sensory input. eg. size, shape, brightness, closeness, etc.

What are Top down factors?

driven by knowledge, expectation, etc. eg. memory, previous experience.

How does bottom up processing work?

You see an object analyse the features and parts into a complex form form perception of the object.

How does top down processing work?

see object use prior knowledge and experience to organise and interpret sensations select features that meet expectations of the stimulus.

Explain bottom up and top down processing based upon the Adelson figure

Bottom up processing - the cones signal two identical colours (sensation) top down processing - takes the fact that there is a shadow into account - the brain compensates this information by making the letter in the shadow as lighter than it really is and we view two colours.

Explain percieved size in terms of both bottom and top processing

Top: understanding depth and distance in relation to other objects Bottom: the size of the bars on the retina

What factors are included in top down processing?

context schemas - enduring knowledge structures experience or learning motivation knowledge of the world expectations Veyr powerful and can dominate perspective

Explain the law of similarity

things that are similar are grouped together

Explain the law of proximity

things near each other appear grouped together

Explain the law of good continuation

stimuli tend to be organised into continuous lines or patterns rather then being percieved as discontinuous elements

Explain the law of closure

every stimulius pattern such that any gaps are seen as closed, complete, whole figure.

Explain the law of familiarity

things are more likely to form groups if the groups appear familiar or meaningful

Explain the law of common fate

things that move together appear to be grouped together.

explain what the gestalt principles exemplify

the way the brain organises perceptual experience to reflect the regularities of nature.

rule of thumb - heuristics

reflect experience used unconsciously occassionally misleading.

depth or distance perception

the organisation of perception in three dimensions

What are the two types of info that are essential in depth perception?

binocular cues (visual input from both eyes) monbocular cues (visual input from one eye)

what are the binocular depth perception cues?

Convergence - how hard your eyes and muscles have to work to look at something eg. something super close to your face - eyes cross and muscles strain = brain percieves it as close object Retina disparity - the difference between the two images in the two eyes

What are the monocular depth perception cues?

Interposition Linear perspective texture gradient shading arial perspective familiar size relative size

Explain interposition (occlusion)

If an object blocks another - then logically the object doing the blocking is closer than the other

Explain Linear perspective

parallel lines meeting together show depth eg. halls, train tracks, etc.

Explain texture gradient

You can see texture up close but distance recedes the patterns

Explain shading

3D objects cast shadows

Explain arial perspective

Objects further away appear fuzzy due to

Explain familiar size

objects being smaller than they should normally be are percieved as being distant

explain relative size

when looking at two objects that are the same (or similar sizes) to one another, people percieve the object that is smaller as further away

perceptual constancies

percieve objects as stable and relatively unchanging despite changes in the stimulation of our sensory receptors.

What are the three types of perceptual constancies

colour constancy size constancy shape constancy

Colour constancy

shape constancy

we recognise an object as having the same shape although we may view it from a different angle or distance eg. opening a door - the shape on your retina is changing, however you don't view it as change in object

Size constancy

objects do not differ in size when viewed from different distances eg. the closer an object - the larger image it casts on our retina

Phantom Limbs

ongoing sensation from a limb that is no longer there. At the sight of amputation - the nerve ending thicken and become more sensitive - reacting to even mild pressure. Somatasensory cortext processes the new - even more intense - info cortical map - increased representation of parts like the tongue, lips, hands, etc.

Prosopagnosia/ face blindness

Inability to recognise faces