Ch. 4: Sensation and Perception Flashcards
What is sensation?
Simple stimulation of a sense organ; the basic registration of light, sound, pressure, odour, or taste as parts of your body interact with the physical world
What is perception?
Occurs in your brain as sensation is registered there; the organization, identification, and interpretation of a sensation in order to form a mental representation
What is transduction?
When sense receptors convert physical signals from the environment into neutral signals that are sent to the central nervous system; physical energy from the world is converted into electrical signals, which are interpreted by the brain to construct a perception of the world
What is sensory adaptation?
Sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current, unchanging conditions
What is psychophysics?
Methods that systematically relate the physical characteristics of a stimulus to an observer’s perception
What is an absolute threshold?
The minimal intensity needed to detect a stimulus in 50% of trials; the simplest quantitative measurement in psychophysics
What is a threshold?
The boundary between two psychological states (awareness and unawareness, perceiving and not perceiving, etc.)
What is sensitivity?
How responsive we are to faint stimuli; often assessed using absolute threshold
What is acuity?
How well we can distinguish two very similar stimuli
What is the just noticeable difference (JND)?
The minimal change in a stimulus (ex. loudness, brightness) that can just barely be detected; depends on the particular sense being detected, the intensity of the original stimulus, the environment, etc.)
What is Weber’s law?
For every sense domain, the change in a stimulus that is just noticeable is a constant ratio of the standard stimulus, over a range of standard intensities (ex. you would likely notice the difference between a 30 g and a 60 g envelope, but not a 2 kg and 2.05 kg package because the needed ratio has not been reached)
What is signal detection theory?
A way of analyzing data from psychophysics experiments that measures an individual’s perceptual sensitivity while also taking noise, expectations, motivations, and goals into account; whether or not a stimuli is perceived depends on the strength of the stimulus and the amount of evidence needed for your perceptual system to decide it is present
What is a decision criterion? What factors influence it?
The amount of evidence necessary for your perceptual system to decide that a stimulus is present; if the sensory evidence exceeds the criterion, the stimulus is perceived regardless of whether it is actually present
- Expectations
- Relative “badness” of an error (ex. sometimes missing a call is better than checking your phone by mistake, and sometimes the opposite)
What are the 2 ways to be right and the 2 ways to be wrong about faint sensory evidence?
- Hit: a radiologist correctly detects cancer on a scan
- Miss: a radiologist doesn’t detect cancer on a scan when it is actually present
- Correct rejection: a radiologist reports that a scan from a healthy person is clear
- False alarm: a radiologist erroneously detects signs of cancer
What are the 2 types of decision criterion, and what do they mean?
Liberal criterion: not much sensory evidence is required; the radiologist identifies cancer whenever there is the slightest indication
Conservative criterion: stronger sensory evidence is required; more unnecessary biopsies are avoided, but more cancer goes undiagnosed
What are the 3 physical dimensions of light waves, and what do they each determine?
Length: determine’s light’s hue
Amplitude: the intensity of a light wave/how high its peaks are; determines brightness
Purity: the degree to which a light source is emitting just one wavelength; determines the saturation/richness of colour
Describe how the eye detects and focuses light.
- Light reaches the eye and passes through the cornea
- The cornea bends the light wave and sends it through the pupil (hole into the eye)
- The iris, a muscle, contracts and relaxes to control the amount of light allowed through the pupil
- Muscles inside the eye control the shape of the lens, which focuses light onto the retina
- The retina, a reflective layer of tissue, receives the light wave/image
What is accommodation, in terms of sight?
The process by which the eye maintains a clear image on the retina; eye muscles make the lens flatter for objects that are far away and rounder for nearby objects
What is myopia?
Nearsightedness; if the eyeball is too long, images are focused in front of the retina
What is hyperopia?
Farsightedness; if the eyeball is too short, images are focused behind the retina
What are the 2 types of photoreceptors cells, and what do they do?
Cones: detect colour, operate under normal daylight conditions, and allow us to focus on fine detail
Rods: become active only under low-light conditions for night vision; more sensitive than cones, but provide no information about colour
What is the fovea?
An area of the retina where vision is clearest and there are no rods at all; the absence of rods decreases the sharpness of vision in reduced light
Why are objects in your peripheral vision less clear?
The light reflecting off them falls outside the fovea, and the lower density of cones there results in a fuzzier image
What are the layers of cells in the retina?
- Innermost: photoreceptor cells (rods and cones)
- Bipolar cells
- Retinal ganglion cells
What are bipolar cells?
Cells in the eyes that collect electrical signals from rods and cones and transmit them to the outermost layer of the retina where retinal ganglion cells are
What are retinal ganglion cells?
Cells in the eye that organize the signals from the bipolar cells and send them to the brain; the bundles of RGC axons form the optic nerve
What is the optic nerve, and why does it create a blind spot?
Bundles of retinal ganglion cells that leave the eye through a hole in the retina; contains neither rods nor cones, and therefore has no mechanism for sensing light
Why do we not usually notice our blind spots?
Our perceptual system automatically fills in the blindspot using knowledge of the colour/texture around the blindspot
Describe how the optic nerve carries neural impulses to the brain.
- Streams of action potentials containing information encoded by the retina travel to the brain along the optic nerve
- Information from the right visual field is relayed to the left hemisphere of the brain while information from the left visual field is relayed to the right hemisphere
- Information travels to the lateral geniculate nucleus (LGN), located in the thalamus of each hemisphere
- The visual signals then travel to the back of the brain to Area V1 (part of the occipital lobe that contains the primary visual cortex)
Which sense does the thalamus not receive inputs from?
Smell
What is the visible spectrum?
The rainbow of hues we can see and their accompanying wavelengths
What are the 3 types of cones, and what are each sensitive to?
L-cones: especially sensitive to long wavelengths
M-cones: especially sensitive to medium wavelengths
S-cones: especially sensitive to short wavelengths
What do the 3 cone types allow the brain to interpret, and how?
- Brightness: signalled by the total amount of activity across all 3 cone types
- Colour: signalled by the relative levels of activity between pairs of cone types
What causes colour vision deficiency?
One cone type (or, rarely, 2-3) is missing
What is a colour afterimage and why does it occur?
A sensory adaptation that occurs when an overload of one colour fatigues the cones that respond to that colour
What is the colour opponent system, and how does it explain the colour aftereffect?
Pairs of cone types (channels) work in opposition:
- L cone channel against the M cone channel
- S cone channel against the M cone channel
When one type of cone is fatigued, the opposing channel is more active in comparison and results in you seeing the “opposite” colour
What happens once the optic nerve carries the neural impulses to Area V1 in the brain?
Information is systematically mapped into a representation of the visual scene; Area V1 is sensitive to edge orientation and its neurons selectively respond to bars and edges in specific orientations
What are the 2 visual streams that visual processing areas are categorized into?
- Ventral (lower) stream
2. Dorsal (upper) stream
What is the ventral visual stream?
The lower visual stream, often called the WHAT pathway because it represents what an object is; travels across the occipital lobe into the lower levels of the temporal lobes and includes brain areas that represent an object’s shape and identity
What is the dorsal visual stream?
The upper visual stream, first known as the WHERE pathway and later called the PERCEPTION FOR ACTION pathway since it is crucial for guiding actions like aiming, reaching, or tracking with the eyes; travels up from the occipital lobe to the parietal lobes and some of the middle/upper levels of the temporal lobes; identifies where an object is, how an object is moving, and lets us perceive spatial relations
What is the 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; we can simultaneously be aware of what an object is, where it is located, and how to pick it up even though those features are represented in different parts of the brain
What is a potential explanation for the binding problem?
Binding neurons, which receive input from other neurons and are involved in representing different features of an object
What is parallel processing?
The brain’s capacity to perform many activities at the same time
What is illusory conjunction?
A perceptual mistake, or binding error, whereby the brain incorrectly combines features from multiple objects
What is Feature-Integration Theory?
Focused attention is not required to detect the individual features that make up a stimulus (colour, shape, size, location, etc.), but it is required to bind those individual features together
What is attention, and how is it involved in illusory conjunctions?
The active and conscious processing of particular information which provides the “glue” necessary to bind features together; illusory conjunctions occur when people cannot pay full attention to the features that need to be “glued” together
What about the brain is responsible for us being able to recognize something when some aspects of it are changed (ex. anew haircut, different lighting/angles, etc.)? What are the 2 possible explanations for this?
Different regions of the ventral stream respond preferentially to different kinds of objects (faces, bodies, scenes, tools, etc.)
- Modular View
- Conceptual Knowledge
What is the modular view when it comes to explaining brain regions that respond preferentially to visual information about certain objects?
Specialized brain areas (modules) detect and represent specific objects because different objects differ in their visual properties (shape, size, etc.)
What is the conceptual knowledge view when it comes to explaining brain regions that respond preferentially to visual information about certain objects?
An object’s visual properties are analyzed in the ventral visual stream, which leads to the activation of conceptual knowledge at higher levels of the ventral stream closer to the front of the brain