Sensetion And Perception Flashcards
Where does sensation come from?
Our environment
For environmental stimuli to be passed onto the brain they have to be converted into what?
A form that the brain could understand (neural impulses), know as transduction
What does lateral geniculate convert light rays to?
Converts light rays to electrical energy by ganglion cells and these signals travel along the optic nerve through lateral geniculate nuclei
We can only see in 2D but out perception of the world is…
In 3D
Why is the image we create in the retina of the eye upside-down and back-to-front?
So we do not directly translate the exact image of the object
Sight is what?
Indirect
The visual information we receive in our eyes doesn’t come directly from the stimulus, but from where?
From the light (electromagnetic radiation formed from oscillated waves of electrical and magnetic energy) reflected directly off it
How much of the electromagnetic spectrum is visible to us?
We only see a very small part
Light travels in waves that can be defined by what?
Their amplitude and wave length
What is the amplitude of light waves?
Height of wave which is perceived as brightness
What is wave length perceived as in relation to light wave?
It is perceived as colour
A small retinal image can be generated from what?
An object which is up close or far away
The eye has many important structures for focusing light on the relevant structures, what are they?
- Cornea
- lens
- retina
What is the cornea?
Front part of the eye where light enters
What is the lens?
Where the light is focused and can change its shape to do so
What is the retina?
The film that you would find on the back of the eye made up of fovea and optic disc and multiple cells
What is the fovea?
A dip in the retina that has a high concentration of specialised neurons that respond to light energy called cones so that sharp and detailed objects are processed and is the black part which is visible in the eye
What is the optic disc?
Where nerves leave the eye and go onto from the optic nerve which is the first part of the pathway to the brain and is the white part which is visible in they eye and you can often see the blood cells radiating out
What are specialised cells used for capturing light known as?
Photoreceptors
What are photoreceptors connected to?
Bipolar cells which are connected to ganglion cells which go into form the optic nerve
There are two types of photoreceptors, what are they?
- a rod
- a cone
They are named for their shape
What are rods
Primarily black and white detectors and do not give any indication about colour or details but instead used in low light and are concentrated in the peripheral areas of the retina and there are around 120 million rods in the human retina
Cones give rise to what?
Colour sensation and detailed high quality visual equity that are connected at the fovea and there are around 6 million cones in the human retina
There are 3 different types of cones so that maximum amount of wavelengths is absorbed, what are they?
- short responds to blue wavelengths
- medium responds to green wavelengths
- long responds to red wave lengths
The three types of cone cells are compared and this gives rise to what?
Colour vision
The destination for almost all visual information is v1 and v2, where is this?
In the visual cortex which sorts and segregates visual information before being passed onto different regions of the Brain for further processing
What are the three main categories of segregation?
- form
- colour
- motion
Area v3 specialised in what?
The form of an object with additional information about the motion
What does v3 contain?
Specialised cells which respond to the motion of particular edges which would correspond to a stationary object that is in one place is tilting or rotating
What does area v4 specialise in?
Colour information (colour which is perceived not the stimulus properties of the object like wavelengths of light) with some information about the form of an object
Area v5 also captures motion but unlike in v3 the cells in v5 will respond to?
The overall motion of an object (speed and direction) with no identity of what the object is
What does the inferno-temporal cortex identify?
Objects and information about shape, colour and form are all integrated
What do visual illusions tell us?
Things about the visual system
Much of perception is problem solving and that the visual system comes up with?
A hypothesis about what is being seen which is top down aspect and the hypothesis is tested using information that comes information rant comes from the stimulus
What is top down aspect?
Knowledge driven
What is the stimulus?
Data driven/ bottom up part of perception
When the data from the top down and bottom up meet what do we get?
We get perception and sight but if we do not have generated the correct hypothesis than another hypothesis is generated and would be tested against the information
This does not reach our consciousness and it is so rapid that we see it as?
Instantaneous
Sometimes we see things which aren’t there and sometimes we fail to see things which should be perfectly visible and this tends to happen when?
The stimulus is not obvious and we become aware of this process- this tells us that there is interpretation and construction of the visual image
What is challenge blindness?
The failure to notice an obvious change
What is intentional blindness?
The failure to notice the existence of an unexpected item
How does challenge blindness and intentional blindness result?
Results as out visual system is resource limited so we have to focus on the salient parts of the visual scene and we do not have the capacity to process everything and send resources to where they are most necessary
How can we see visual illusions?
Due to contrast (the difference in brightness and colour that differentiates a colour from its background and from other objects in the visual scene) contrast effects can create visual illusions
What is the match bands?
An illusion which shows bands which all have the same brightness but what we perceive that they are brighter on the left so our perceptions does not correspond to the physical properties
In a Hermann Grid we perceive?
That there are spots on the grid but in reality they are not there and they occur because of contrast and our perceptual system is filling in the gaps between because it believes there should be more contrast there
The visual system tries to simplify things as
It emphasises differences
In colour sensation what is hue?
Technical term to describe colour
In colour sensation what is brightness?
How dark or light an object is
In colour sensation what is saturation?
How vivid the colour is
There are two main historical theories about colour perception- what are they?
- Young- Helmholtz theory
2. Opponent- Process theory
What is the young-Helmoltz theory?
Trichromatic theory of colour vision- three separate pathways for processing colour I.e one for blue, red and green and each pathway would extend to the brain but the theory does not explain how we like colours like yellow or colour mixing
What is the opponent-process theory?
Colours are processed in pairs and their is an antagonistic relationship so if the red part was excited then the green part would be inhibited
Both theories (young and opponent)
Feed into modern understanding of colour perception
The opponent-process theory is accurate to what we know as?
The information that we receive from the photoreceptors is recoded into pairings
There are three types of pairings- what are they?
- red/green
- blue/yellow
- black/white
Colour contrast allows us to?
See these theories in action
Colours induce their antagonists in?
Neighbouring areas
Negative colour imaging provides evidence that?
Colours are presented in pairs
Perception of shapes depends on?
Feature detection
In perception of shapes in area v1 there are specialised cells which are?
Feature detectors and are tuned to respond to specific feature of an object I.e one cell which responds to a horizontal line that is located in the upper right corner of the visual field
Visual receptors tend to respond best to?
A line or an edge and other cells assemble the visual output and are passed onto other cells
A specifi feature a cell responds to is known as?
The cells receptive field and its optimal output is what defines its receptive field and different cells have different receptive fields
Torton Wiesel and David H. Hubel were pioneers in examining?
The roles of single cells in the visual cortex
The cat experiment showed?
That the more of a firing response when the cell was presented with a certain stimuli but there was not the same response when there was a less preferred stimulus
The recognition of form begins with?
The detection of simple features and the importance of theses tasks is highlighted by visual search tasks
What are visual search tasks?
Where we have to determine whether a particular target is present or not and when the target differs from the distractors in one aspect it is easy to detect but it differs in a number of ways, it is difficult to tell whether the target is present or not
The detection of features is one aspect of the perception of objects and forms part of the bottom up processing but ?
There are constraints posed by our expectations and experiences that feed into our perception of objects
Most stimuli
Is not ambiguous and we can see the process going on when there is ambiguity and we have to segregate what is the object of importance and what is the background known as figure ground segregation
The perceived has to
Organise visual information
What does the visual system pathway include?
- optic nerve
- retina
- cornea
- lateral geniculate nuclei
- visual cortex
Our visual experience is…
Constructed and interpreting the information we receive - it is in the part of the brain where sensation happens
Our sense organs are responsible for?
Sensation by capturing environment stimuli
Our eyes are designed to?
Captors light energy which passes the information onto the cortex of the brain where the information is organised interpreted and is given meaning
