chapter 3 Sensation & Perception Flashcards
What is Psychophysics?
the relating of mental experiences with physical reality; a specialized sub-domain of research on sensation & perception
What are the two issues of interest in psychophysics?
1) Detection of sensory experience: telling us what info a person can sense outside of themselves
2) Discrimination of sensory experiences: how much the world needs to change before a person registers the difference
What is the minimal amount of energy needed to detect a stimulus called?
Sensory threshold, if detectable
more than 50% = supraliminal
less than 50% = subliminal
What is the smallest amount of physical change a person can detect called?
the JND, just noticeable difference
Webers Law of JND?
earliest attempt to capture the JND. k = change in I/ I.
- more simply stated, the size of the just noticeable difference (i.e., delta I) is a constant proportion of the original stimulus value.
- For example: Suppose that you presented two spots of light each with an intensity of 100 units to an observer. Then you asked the observer to increase the intensity of one of the spots until it was just noticeably brighter than the other. If the brightness needed to yield the just noticeable difference was 110 then the observer’s difference threshold would be 10 units (i.e., delta I =110 - 100 = 10). The Weber fraction equivalent for this difference threshold would be 0.1 (delta I/I = 10/100 = 0.1)
Fechner’ Law of JND
Fechner’s law states that the subjective sensation is proportional to the logarithm of the stimulus intensity. … For example, if a stimulus is tripled in strength (i.e., 3 x 1), the corresponding perception may be two times as strong as its original value (i.e., 1 + 1).
-denoted. S = k log R”.
Stevens Power Law of JND’s
The general form of the law is
-ψ(I) =k I^a
psi (I)=kI^{a},}
where I is the magnitude of the physical stimulus, ψ(I) is the subjective magnitude of the sensation evoked by the stimulus, a is an exponent that depends on the type of stimulation, and k is a proportionality constant that depends on the units used.
When we judge differences between symbols more rapidly when they differ considerably on some symbolic dimension such a value, this is called–
The Symbolic Distance Effect
Semantic Congruity Effect
the condition in which a person’s decision is faster when the dimension on being judged matches or is congruent with the implied dimension
Retina
the layer of the eye covered w/ the rods & cones that initiate the process of visual sensation & perception
Sensation
the reception of physical stimulation & encoding of it into the neutrons system
Explain the process by which light enters eye and is converted into sensory images
Light waves enter the eye, the light is then focused by lens & inverted, then projected onto the retina. The retina has 3 layers of neutrons: 1)rods & cones 2) bipolar cells and 3)ganglion cells.
Rods & Cones
are neutrons stimulated by light, beginning the process of vision. Patterns of neural firing from these cells pass on to a second layer- the bipolar cells.
- Rods don’t help with color vision, which is why at night, we see everything in a gray scale. The human eye has over 100 million rod cells.
- Cones require a lot more light and they are used to see color
Bipolar Cells
these cells collect the messages from the rods and cones & move them along to a third layer- the ganglion cells
Ganglion Cells
these cell’s axons coverage at the rear of the eye, forming bundles of fibres that make up the optic nerve. They receive the messages from the bipolar cells.
Contralaterality Principle
binocular pathway of info flow from eyes into the visual cortex, and the left hemisphere processes the images that come from the right side and vice versa.
Perception
the process if interpreting & understanding sensory information; that act of sensing then interpreting information
How do Saccades and Fixations work?
the eyes jerk & sweep from one point to another in fast movements-saccades-taking anywhere from 25ms-175ms, plus taking about 200ms just to plan these movements. When your eyes are focused on a singular point these are called the fixations, that happen in between the saccades.
Change Blindness
our failure to notice changes in visual stimuli when those changes occur during a saccade
Inattention Blindeness
we sometimes fail to see an object we are directly looking at because our attention is directed elsewhere
Synethsesia
a condition in which a person will have inappropriate & involuntary sensory experiences in addition to typical sensory experience
-Projectors: those whose extra sensory experiences appear to them as ‘out in the world’
-Associators: theirs are in their mind
Why?: 1) perhaps a lower ability to suppress inappropriate feedback loops in perceptual processing
2) perhaps because there is an incomplete pruning of extra cortical connections during development
Photism
most common form of synethsesia where one experiences colour when reading words or letters
Visual Sensory Memory
the short duration memory system specialized for holding visual information, lasting no more than about 250ms to 500ms
Visual Persistence
the perceptual phenomena in which a visual stimulus still seems to be present even after its termination, usually a few hundred ms to a few seconds.
Span of Apprehension/Attention
the number of items recallable after any short duration- span of ‘immediate memory.’
Whole report condition vs Partial Report condition (Sterlings experiment)
WRC: when the participants are asked to recall as many letters as the can from the total 12 shown (avg =4.5)
PRC: when the participants are asked to recall only a select row of letters (success was 76% meaning visual memory for entire display is also 76%, we just can’t recall it all)
Icon
what we call the contents of the iconic memory, the visual image that resides in iconic memory
