Perception Flashcards
What is psychophsyics?
Psychophysics is a scientific method for investigation of relationships between physical stimuli and psychological which marks the beginning of experimental psychology
What is the absolute threshold?
Absolute threshold is the minimum stimulus detected reliably from no stimulus i.e. detection of difference from zero
What is absolute detection?
Absolute detection is really a special case of difference detection
What is difference detection?
Difference detection wants to establish what increase in intensity is required for people to determine a difference exists between two people
What is a standard stimulus?
Standard stimulus gets people to detect if another comparative stimulus is more than the standard.
What is the difference threshold or ‘Just Noticeable Difference’ (JND) ?
JND is the minimum difference in stimulus intensity necessary to tell two stimuli apart. This depends on the magnitude of the stimuli
What is the Weber - Fechner Law?
Weber - Fechner Law is the change in intensity divided by intensity
What does the Weber-Fechner Law state?
This law states that JND is a constant proportion of standard stimulus intensity
What is the Weber fraction for light intensity, sound intensity and salt taste?
Light intensity- 0.079
Sound intensity - 0.048
Salt taste - 0.083
What do signal detection experiments involve?
Signal detection experiments involve discriminating the presence of a stimulus from background noise
What is visible light?
Visible light is the portion of the electromagnetic spectrum that is seen by humans
What is visual acuity?
Visual activity is the ability to see fine detail
How does light enter the eye?
Light reflected from a surface enters the eye via the transparent cornea bending to pass through the pupil at the centre of the coloured iris
Where is the light focused on the eye?
Light is focused onto the back of the eye, the retina, by a lens that changes shape depending on the distance of the object we are trying to focus upon.
What is the retina made up of?
The retina is made up of 120 million photoreceptors
What are photoreceptors?
Photoreceptors are sensory cells that respond to light
What do photoreceptors do?
Photoreceptors influence the specialised neurons that signal the brain’s visual centres through their bundled axons, which make up the optic nerve
What does the optic nerve do?
The optic nerve creates the blind spot
The retina has a small dip in it called the fovea, what is the fovea?
The fovea is the area responsible for high acuity vision i.e. vision is clearest at the fovea
What are the two types of photoreceptors?
rods and cones
How many types of cones are there and what do they do? and what do they allow us to perceive?
There are three different types of cones that respond to different wavelengths of light which allow us to perceive colour
What is the fovea made up of?
Fovea is made up of cones
What are rods sensitive to and what does this mean?
Rods are more sensitive to light which makes them useful in dark situations. They DO NOT provide info on light
What are the vast majority of our photoreceptors?
The vast majority of our photoreceptors are rods
Photoreceptors also connect to retinal ganglion cells. What do the axons on the retinal ganglion cells form?
Axons of these retinal ganglion cells form the optic nerve. There are no photoreceptors on the retina where the optic nerve is making a blind spot.
What happens to the retinal image when it passes through the lens?
The retinal image is inverted in passing through the lens. The image is therefore topographic (map-like) reflecting the real world spatial relationship
What do photoreceptors respond to?
Photoreceptors respond to different wavelengths and intensities of electromagnetic radiation
What are receptive fields?
Receptive fields are regions of sensory surface that when stimulated causes a change in the firing rate of a neuron
What types of cells do receptive fields have?
You can have off centre or on centre cells
Where does each photoreceptor receive light from?
Each photoreceptor receives light from a specific part of the visual field so its receptive filed corresponds to a specific part of the visual field
What is the receptive field of a retinal ganglion cell determined by ?
The receptive field of a retinal ganglion cell is determined by the positions of the photoreceptors to which it connects
What are ganglion cells sensitive to?
Ganglion cells are sensitive to differences between illumination in the centre and surround portions of its receptive fields
What do simple cells have?
Simple cells have longer receptive fields than ganglion cells, they respond to edges of a certain orientation in a certain position
What do complex cells combine?
Complex cells combine input from many simple cells with the same orientation tuning and adjacent receptive fields
What do hypercomplex cells combine?
Hypercomplex cells combine input from many complex cells to respond to increasingly refined features
What do simple, complex and hypercomplex cells detect?
Simple, complex and hypercomplex cells detect edges of increasing complexity whilst having progressively larger receptive fields. Its a bottom up hierarchy.
What can feature detectors respond to?
Some feature detectors respond to a certain orientation of a line whilst others respond to colour, direction or speed of motion
What is motion?
Motion is a powerful cue for alerting and orienting attention and its also an important form for perception
Motion perception is relative. What does this mean?
This means the figure is perceived to move against a stationary background
What is space constancy?
Space constancy is when we perceive space as a constant and this is the case when we move our eyes very quickly like in saccades
What is saccadic inhabition?
Saccadic information is the reason why when our eyes move, the world stays stable even though the image whips across our retina.
Space constancy means we factor out self-generated movement to perceive only movement arising in the world. How do we do this?
We do this by monitoring eye muscle system for sensory info i.e. we send a command, the eyes move, and then the sensory info that comes back about the position or the amount of contradiction of a particular occulier muscle
We have a copy of a motor signal that goes out (efferent). What does this mean?
We use it to compare the sensory info that comes back with what we were expecting based upon the signal we issued.
How can we see colour?
Colour is purely perceptual. We have a range of electromagnetic radiation or spectrum and within that we have photo receptors that are able to detect certain wavelengths- we call this visible light.
What is the colour of an object or substance determined by?
The colour of an object or substance is determined by the wavelengths of light that it reflects
What are the two types of photoreceptors we have?
Rods and cones
Rods are very light sensitive. What do they all contain?
They all contain the same photopigment rhodopsin
What do rods provide?
Rods provide low acuity, light sensitive, peripheral vision which is monochromatic
Where are cones? and what does their placement mean?
Cones are tightly placed in the central fovea, giving high acuity colour vision
What are the three types of cone? and how do they differ?
The three types of cones have different absorbance spectra - blue (small cone) green (medium cone) and red (large cone)
What is trichromacy?
Trichromacy is the combination of responses across the cone types which leads to the perception of all colours
What does binocular disparity require?
Binocular disparity requires two eyes to determine the differences in the images on the left and right
What does binocular disparity mean?
Binocular disparity means that the images on the two retina are different. They point in the same direction and have overlap.
What is stereoscopic vision?
Stereoscopic vision is the difference between the image that the left and the right eye has
What is motion parallax?
Motion parallax is a dynamic monocular retinal depth cue. It relies on movement to give info about distance of objects
What is static (pictorial) monocular cues?
Static pictorial monocular cues are available when viewing static scene such as a picture through one eye
What are different depth cues?
- interposition (object blocking another object)
- height in scene
- blur (the further away you are typically the more blurry things appear to be)
- size (e.g interposition which tells us the rank order of objects)
- perspective (make assumptions that converging lines are parallel)
- texture gradient (brain assumes constant grain size)
What is size constancy?
Size constancy describes our tendency to take distance into account when estimating object size i.e. far objects do not seem as small as they should do, because we scale them up perceptually
How can the brain calculate the distance to the point of fixation?
By monitoring the convergence angle of the eyes, the brain can calculate the distance to the point of fixation
What are the laws of perceptual organisation?
simplicity
similarity - similar things are grouped together
proximity - near things group together
good continuation - points on straight or smooth lines belong together
closure
common fate - things that move together belong together e.g. flock of birds
meaningfulness/familiarity - things are more likely to form groups if those groups are meaningful
What is synaesthesia?
Synaesthesia is a condition in which a person experiences sensations in one modality when a second modality is stimulated
There are two types of synesthetes. What are they?
Associater and projector synesthetes
What is an associater synesthete?
An associater synesthete is when a person may see an ‘s’ and have a sensation of red
What is projector synesthete?
A projector synesthete is when a colour is actually projected in the inner mental imagery
