Midterm 2.2 Flashcards
sensation and perception
sensation is the simple stimulation of a sense organ. it is the basic registration of light, sound, pressure, odour, or taste as parts of your body interact with the physical world
perception occurs in brain as sensation is registered there. it is the organization, identification, and interpretation of a sensation in order to form a mental representation
transduction: when sense receptors convert physical signals from the environment into neural signals that are sent to the CNS, this is how sensory receptors communicate with the brain
sensory adaptation
sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current (unchanging) conditions
pyschophysics
methods that systematically relate the physical characteristics of a stimulus to an observer’s perception
the simplest quantitative measurement is absolute threshold: the minimal intensity needed to just barely detect a stimulus in 50% of the trails
absolute threshold is useful for assessing sensitivity: how responsive we are to faint stimuli
acuity: how well we can distinguish two very similar stimuli, such as two tones that differ slightly in loudness
the just noticeable difference (JND) is the minimal change in a stimulus that can just barely be detected -> not a fixed quantity, it depends on the particular sense being measured, as well as on the intensity of the original stimulus
ex. observer is a dark room is shown a light of fixed intensity, called the standard (S), next to a comparison light that is lsightly brighter or dimmer than the standard. When S is very dim, observes can perceive even a very small difference in brightness between the two light: the JND is small. But if S is bright, a much larger increment is needed to detect the difference: The JND is larger
Weber’s law: for very sense domain, the change in a stimulus that is just noticeable is a constant proportion despite variation in intensities (ratio between JND and standard stimulus is constant, unless standard takes extreme values)
ex. 25g evelope vs 50 gram, can feel difference, but 10kg and 25kg, probably detect no difference
signal detection
critical assumption for measuring absolute and difference thresholds: threshold exists!
an approach to psychophysics called signal detectiontheory holds that the response to a stimulus depends both on a person’s sensitivity to the stimulus in thr presence of noise and on a person’s decision criterion
observers consider the sensory evidence evoked by the stimulus and compare it with an internal decision criterion
purity
third dimension that refers to degree to which a light source is emitting just one wavelength or a mixture, influences how colour is perceived
some synthetic light sources produce light that is pure (one wavelength), hve high saturation (rich colours)
eye detects and focuses light
light passes cornea, bends light wave to pupil surrounded by iris (controls amount of light into eye), muscles control shape of lens to bend light to retina (layer of light-sensitive tissue)
muscles change change of lens to focus objects at different distances, making the lens flatter for obects that are far away or rounder for nearby objects (accomodation, the process whereby the eye maintains a clear image on the retina)
if eyeball too long/short, lens will not focus image properly
too long is image focused in front of retina, nearsightedness (myopia)
eye too short, image focused behind retina, farsightedness (hyperopia)
light converted into neural impulses
two types of photoreceptor cells in retina
cones detect colour, operate under normal daylight conditions, allow fine detail focus
rods become active only under low-light conditions for night vision (much more sensitive)
fovea: area of the retina where vision is clearest and there are no rods at all; absence of rods decreases sharpness of vsion in redeuced light, but benefit is enhanced sensitivity to faint light in the rest of the retina outside the fovea (the periphery)
ex. look a little off to the side instead of directly on dim stars so that the image iwll fall not no the rod-free fovea but on some other part of the retina that contains many highly sensitive rods
more rods than cones
retina
photoreceptor cells form innermost layer, beneath a layer of transparent neyrons called the bipolar and ganglion cells.
bipolar cells collect electribcal signals from the rods and cones and transmit them to the outermost layer of the retina, where neurons called retinal ganglion cells (RGCs) organize the signals and send them to the brain
bundled RGC form optic nerve, leaves thorugh a hole in the retina, contains no rods or cones -> blind spot
info first goes to lateral geniculate nucleus (LGN) in thalamus of each hemisphere (thalamus receives inputs from all senses except smell), from LGN visual signals travel to the back of the brain to area V1, the part of the occipital lobe that contains the primary visual cortex
extra info
temporary colour dificiency: colour afterimage: form of sensory adaptation
explanation: colour-opponent system: pairs of cone types (channels) work in opposition: the L-cone channel against M-cone channel, and S-cone against M-cone, tire cones out (fatigue)
neural systems for perceiving shape
perceiving shape depends on the location and orientation of an object’s edges
area v! is sensitive to edge orientation
neurons in the primary visual cortex selectively respond to bars and edges in specific orientations in space
visual receptive field: region of the visual field to which each neuron responds, is small for neurons in V1
area v1 contains populations of neurons, each tuned to respond to edges oreinted a particular way in a particular location in space (some neurons fire when we perceive horizontal edge)
neuron pathways
visual info spreads out and is processed in many brain areas
neurons in V1 and its beighbouring brain regions respond to only a small region of the visual field (they have small receptive fields) and are tuned to relatively simple features like edges
visual processing areas can be simplified into two functionally distinct pathways or visual steams
- ventral stream (lower) travels across occipital lobe into lower levels of temporal lobess, includes brain areas that represent an object’s shape and identity
- the dorsal (upper) stream travels up from occipital lobe to parietal lobes and includes brain areas that identify where an objecct is and how it is moving (where pathway, spatial relations)
binding problem: how the brain links features together so that we see unified objects in our visual world rather than free-floating or miscombined features
binding individual features into a whole
parallel processing is the brain’s capacity to perform multiple activities at the same time
parallel processing of these different features must somehow be integrated into a single, unified perception of an object
illusory conjunctions: perceptual mistakes
discovered errors in binding that reveal important clues about how the process works
one error includes illusory conjunction, a perceptual mistake whereby the brain incorrectly combines features from multiple objects
why do illusory conjunctions occur? feature-integration theory: holds that focused attention is not required to detect the individual features that make up a stimulus, but it is required to bind those individual features together. From this perspective, attention, which is the active and conscious processing of particular information, provides the flue necessary to bind features together
