Sensation and perception Flashcards
define sensation
simple stimulation of a sense organ
basic registration of light, sound, pressure, smell or taste as parts of the body interact with the physical world
Define perception
organisation, identification & interpretation of a sensation in order to form a mental representation
How do sensory receptors communicate with the brain?
transduction
Define transduction
- when receptors convert physical signals from the environment into neural signals that are sent to the central nervous sytem
What energy is the eye uniquely sensitive to?
light
What energy is the skin uniquely sensitive to?
mechanical pressure
What is the illusion of perception?
- we can only see a small portion of the electromagnetic frequencies > those that generate visible light
- we can seem them because we have visual receptors for those frequencies
What is sensory adaptation?
sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current (unchanging) conditions
What causes sensory adaptation?
- our sensory systems respond more strongly to changes in stimuli than to constant stimulation
- changes in stimuli often signal a need for action
- sensory signals that don’t change usually don’t require any action & are discarded by body
What is psychophysics?
methods that systematically relate the physical characteristics of a stimulus to an observer’s perception
What is the simplest quantitative measurement in psychophysics?
absolute threshold: the minimum intensity needed to just barely detect a stimulus in 50% of the trials
What is a threshold in psychology?
A boundary btw 2 psychological states
(eg. unawareness and awareness)
What does the absolute threshold assess?
- sensitivity: how responsive we are to faint stimuli
- acuity: how well we can distinguish 2 very similar stimuli
What is the Just Noticeable Difference (JND)?
- the minimal changes in a stimulation that can barely be detected
- not a fixed quantity: depends on sense being measured
State Weber’s law
- For any sense domain, the change in a stimulus that’s just noticeable is a constant proportion despite variation in intensities
- for any sensory domain the ratio btw JND and standard stimulus is a constant value
What is signal detection theory?
The response to a stimulus depends on
1. a person’s sensitivity to the stimulus in the presence of noise
2. person’s decision criterion
What is light?
waves of energy that vary in height and wavelength
What are the 3 physical dimensions light waves vary on?
- Length: hue of wave & what we perceive as color
- amplitude: how high peaks are, what we perceive as brightness
- purity: if light is emitting just 1 wavelength or a mix of wavelengths, affects color perception
In what order does the eye detect light?
Cornea > iris > retina >
What is the cornea?
- first outer layer of eye
- bends light wave and sends it through the pupil
What is the iris?
- colored part of the eye
- translucent donut shaped muscle that controls the size of the pupil & hence the amount of light that enters the eye
- behind the iris, a muscle controls shape of lens to bend light & focus it onto retina
What is the retina?
- layer of light sensitive tissue lining the back of the eyeballs
- interface btw light outside of body and the world of vision in the central nervous system
- muscle changes the shape of the lens to focus on objects at diff. distances
What is the process of visual accommodation?
- process whereby the eye maintains a clear image on the retina
What happens when the eyeball is too long?
images are focused in the front of the retina > myopia (nearsightedness)
What happens when the eyeball is too short?
images are focused behind the retina > hyperopia (farsightedness)
What are the 2 types of photoreceptor cells in the retina?
- cones
- rods
What are cones?
- detect colors
- operate under normal daylight conditions
- allow us to focus on fine details
What are rods?
- become active only under low light conditions /night vision
- more sensitive photoreceptors than cones but provide no info about color & sense > only shades of gray
- 120M distributed evenly across retina except middle
What is the area of the retina where there are no rods ?
Fovea: area where vision is clearest
- absence of rods means less sharpness of vision in low light but enhanced sensitivity to faint light in the rest of retina
- cones are densely packed in fovea
What are the 3 layers of the retina?
- Photoreceptor cells (rods, cones): innermost layer
- Bipolar cells: collect electrical signals from rods and cones and transmit them to outermost layer of retina
- Retinal ganglion cells: organise signals and send them to the brain
What forms the optic nerve?
- bundled Retinal ganglion cells form optic nerve
- optic nerve has no rods or cones > no mechanism for sensing light
What is a blind spot?
location in visual field that produces no sensation on the retina
Why don’t we notice blind spots?
Because our perceptual system automatically fills in using knowledge (color, texture) around blind spot
How does the optic nerve carry neural impulses to the brain?
- streams of action potentials containing info encoded by retina, travel along optic nerve
- info first goes to Lateral geniculate nucleus (thalamus)
- from LGN visual signals travel to Area V1 at back of brain
What is Area V1?
- part of occipital lobe that contains primary visual cortex
- contains neurons each tuned to respond to edges oriented a particular way in a particular location in space
Who discovered that the perception of color is created by the brain?
Isaac Newton 1670
What are the 3 types of cones?
- L-cones: sensitive to long wavelengths
- M-cones: sensitive to medium wavelengths
- S-cones: sensitive to short wavelengths
What do disorders where cone(s) is missing cause?
color vision deficiency or color blindness
What is the color opponent system?
- pairs of cone types work in opposition: L-cone against M-cone and S-cone against M-cone
What is the visual receptive field?
region of visual field to which each neuron responds
What are the 2 visual streams?
- ventral stream
- dorsal stream
What’s the ventral stream?
- travels across occipital lobe into lower levels of the temporal lobes & includes brain areas that represent an object’s shape & identity
> represents “what” an object is
What is the dorsal stream?
travels up from occipital lobe to parietal lobes & includes brain areas that identify where an object is & how it’s moving
How are the ventral & dorsal streams functionally distinct?
- one stream may be damaged & the other intact but the 2 streams must still work together during visual perception
> to integrate perception for identification (ventral)
> to integrate perception for action (dorsal)
What is visual form agnosia?
inability to recognize objects by sight
What is the binding problem?
how brain links features together so that we see unified objects in our visual world, rather than free floating/mismatched items
What is the theory linked to the binding problem?
Binding neurons: neurons in ventral visual stream that receive coincidental input from other neurons involved in representing diff. features of an object
How are individual features bound into a whole?
specialised feature detectors in diff. parts of the visual system analyse each of the multiple features of a visible objects: orientation, color, shape
What is parallel processing?
brain’s capacity to perform multiple activities at the same time
What is an illusory conjunction?
perceptual mistake whereby the brain incorrectly combines features from multiple objects