Ch. 7-8 Flashcards
attention
any of the very large set of selective processes in the brain; to deal with the impossibility of handling all inputs at once, the nervous system has evolved mechanisms that are able to bias processing to a subset of things, places, ideas, or moments in time
attention can be…
external or internal; overt or covert
external attention
attention to stimuli in the world
internal attention
our ability to attend to one line of thought as opposed to another or to select one response over another
overt attention
directing a sense organ at a stimulus
covert attention
pay attention to something while looking elsewhere
selective attention
the form of attention involved when processing is restricted to a subset of the possible stimuli
reaction time (RT)
a measure of the time from the onset of a stimulus to a response
cue
a stimulus that might indicate where (or what) a subsequent stimulus will be; can be valid (giving correct information), invalid (incorrect), or neutral (uninformative)
exogenous cue
in direction attention, a cue that is located out (exo) at the desired final location at attention
endogenous cue
in directing attention, a cue that is located in (endo) or near the current location of attention
stimulus onset asynchrony (SOA)
the time between the onset of one stimulus and the onset of another
inhibition of return
the relative difficulty in getting attention (or the eyes) to move back to a recently attended (or fixated) location
the spotlight of attention
- attention could be deployed from spot to spot
- might move in a manner analogous to the movements of our eyes
- best evidence suggests that attention is not moving from point to point in the brain in the way a physical spotlight would move across the world
visual search
a search for a target in a display containing distracting elements
target
the goal of a visual search
distractor
in a visual search, any stimulus other than the target
set size
the number of items in a visual display
- it is harder to find a target as the set size increases
to measure the efficiency of a visual search
- often ask how much time is added for each item added to the display
- measures the RT required for the observer to say “yes” if the target is present or “no” if there is no target in the display
feature search
visual search for a target defined by a single attribute, such as a salient color or orientation
salient
the vividness of a stimulus relative to its neighbors
parallel search
visual search in which multiple stimuli are processed at the same time
search is inefficient when…
the target and distractors in a visual search task contain the same basic features
serial self-terminating search
a search from item to item, ending when a target is found
guided search
search in which attention can be restricted to a subset of possible items on the basis of information about the target item’s basic features
conjunction search
search for a target defined by the presence of two or more attributes
prime
a stimulus that might make it easier or faster to respond to a subsequent stimulus
scene-based guidance
information in our understanding of scenes that helps us find specific objects in scenes
anchor objects
typically a relatively big object that provides information about the location of other objects
binding problem
the challenge of tying different attributes of visual stimuli (e.g., color, orientation, motion), which are handled by different brain circuits, to the appropriate object so that we perceive a unified object
feature integration theory
Anne Treisman’s theory of visual attention, which holds that a limited set of basic features can be processed in parallel preattentively, but other properties, including the correct binding features to objects, require attention
preattentive stage
the processing of a stimulus that occurs before selective attention is deployed to that stimulus
- automatic
- feature search
- parallel processing
illusory conjunction
an erroneous combination of two or more features in a visual scene
rapid serial visual presentation (RSVP)
an experimental procedure in which stimuli appear in a stream at one location (typically the point of fixation) at a rapid rate (typically about 8 per second)
attentional blink (AB)
the tendency not to perceive or respond to the second of two different target stimuli amid a rapid stream of distracting stimuli if the observer has responded to the first target stimulus 200-500 milliseconds before the second stimulus is presented
- fishing with a net analogy
priority map
a hypothetical neural representation of visual space in which the activity at each point reflects how much that location (or object) will attract attention
lateral intraparietal area (LIP)
a brain region, present in both parietal lobes, that serves an important role in the control of visual attention
frontal eye fields (FEF)
brain regions in both frontal lobes that help to coordinate visual selective attention with the movement of the eyes
superior colliculus (SC)
a structure in the midbrain that is important in initiating and guiding eye movements
important candidates for priority maps
LIP, FEF, and SC
fusiform face area (FFA)
a region of extrastriate visual cortex in humans that is specifically and reliably activated by human faces
parahippocampal place area (PPA)
a region of extrastriate visual cortex in humans that is specifically and reliably activated more by images of places than by other stimuli
response enhancement
an effect of attention on the response of a neuron in which the neuron responding to an attended stimulus gives a bigger response
sharper tuning
an effect of attention on the response of a neuron in which the neuron responding to an attended stimulus responds more precisely
- ex. a neuron that responds to lines with orientations from -20 degrees to +20 degrees might shift to respond strongly to -10 to +30 degree lines
different neurons…
perform different parts of the task of attending, and each subtask may require a different type of change in neuronal responses
Reynold’s and Heeger’s “normalization” theory
says that the current response of a neuron is the product of that neuron’s built-in receptive field and the effects of attention; this product must then be “normalized” by neural suppression
complete inattention would be…
something near to functional blindness because one would not be able to recognize objects or find what they are looking for without attention
visual-field defect
a portion of the visual field with no vision or with abnormal vision, typically resulting from damage to the visual nervous system; attentional equivalent to a loss of an ability for attention
neglect
in reference to a neurological symptom, in visual attention: 1) the inability to attend or respond to stimuli in the contralesional visual field (typically, the left field after right parietal damage), 2) ignoring half of the body or half of an object
can assess neglect with a “line cancellation test”
- patient is given a piece of paper full of lines and asked to draw an intersecting line through each one
- would cross lines on one side, but those on the other side are overlooked
contralesional field
the visual field on the side opposite a brain lesion
extinction
in reference to visual attention, the inability to perceive a stimulus to one side of the point of fixation in the presence of another stimulus, typically in a comparable position in the other visual field
ipsilesional field
the visual field on the same side as a brain lesion
Balint syndrome
a disorder where everything except the current object of attention seems to be blocked from conscious perception
reachspace
a region of visual space that is within arm’s reach: bigger than most objects, smaller than a typical scene, and critically positioned where the arms can reach
peripersonal space
that part of the world that is near your body— especially, your hands
two pathways to scene perception
selective and nonselective pathway
selective pathway
- spotlight of attention
- specific locations of objects are selected for the processing that allows for binding and object recognition
nonselective pathway
visual scene outside the current spotlight
ensemble statistics
the average and distribution of properties like orientation or color over a set of objects or over a region in a scene; represent knowledge about the properties of a group of objects
- know this information without knowing the properties of the individual objects
proto-object
a term used to refer to object-like stimuli before they are attended and recognized
spatial layout
the description of the structure of a scene (e.g., enclosed, open, rough, smooth) without reference to the identity of specific objects in the scene
gist
the essential or primary character of a scene; in vision, typically refers to information that can be gleaned in a very brief glimpse, without voluntary eye movements
change blindness
when one scene is replaced by another version of the same scene, observers may be unable to report what changed between the two versions
- maybe we don’t see changes when they don’t change the gist of the scene
inattentional blindness
a failure to notice, or at least report, a stimulus that would be easily reportable if it were attended
motion aftereffect (MAE)
the illusion of motion of a stationary object that occurs after prolonged exposure to a moving object; caused by opponent processes for motion detection
interocular transfer
the transfer of an effect (such as adaptation) from one eye to the other
middle temporal area (MT) (V5)
an area of the brain thought to be important in the perception of motion
induced motion
ex. thinking that the vehicle you are in is moving when watching something else outside of the vehicle actually move
Reichardt’s model
- need multiple neurons to detect motion
- solves the aperture problem by having another set of neurons that each listens to several V1 neurons and integrates their potentially conflicting signals (global-motion detector)
apparent motion
the illusory impression of smooth motion resulting from the rapid alternation of objects that appear in different locations in rapid succession (ex. animations)
aperture
a window-like opening that allows only a partial view of an object
correspondence problem
in reference to motion detection, the problem faced by the motion detection system of knowing which feature in Frame 2 corresponds to a particular feature in Frame 1; how your brain solves the puzzle of matching up all the different pictures your eyes see, so you can see the world as one smooth, continuous picture
aperture problem
the fact that when a moving object is viewed through an aperture (or a single receptive field), the direction of motion of a local feature or part of the object may be ambiguous
- a different detector may win this competition when an object is viewed through an aperture than would win if we could see the whole object
hub for motion processing
middle temporal area (MT) and medial superior temporal area (MST)
first-order motion
the motion of an object that is defined by changes in luminance (reflected light)
luminance-defined object
an object that is delineated by differences in reflected light
second-order motion
the motion of an object that is defined by changes in contrast or texture, but not by luminance (nothing actually moves)
texture-defined object/contrast-defined object
an object that is defined by differences in contrast, or texture, but not by luminance
double dissociation
the phenomenon in which one of two functions, such as first- and second-order motion, can be damaged without harm to the other and vice versa
optic array
the collection of light rays that interact with objets in the world that are in front of a viewer
optic flow
the changing angular positions of points in a perspective image that we experience as we move around the world
focus of expansion (FOE)
the point in the center of the horizon from which, when we’re in motion, all points in the perspective image seem to emanate
Gibson derived a number of optic flow heuristics that the visual system might use to navigate
- mere presence of optic flow indicates locomotion
- lack of flow is a signal that you are stationary
- outflow –> flow toward the periphery; indicates that you are approaching a particular destination
- inflow indicates retreat
- focus of expansions tells you where you’re going to or coming from
time to collision (TTC)
the time required for a moving object to hit a stationary object; TTC = distance / rate
tau
information in the optic flow that could signal time to collision (TTC) without the necessity of estimating either absolute distances or rates; the ratio of the retinal image size at any moment to the rate at which the image is expanding; TTC proportional to tau
biological motion
the pattern of movement of living beings; helps us identify both the moving object and its actions
motion-induced blindness (MIB)
- motion can make you temporarily blind
- if you carefully fixate a central target, stationary targets in the periphery will simply disappear when a global moving pattern is superimposed
- somewhat related to the Troxler effect
- if the eye muscles are temporarily paralyzed, the entire visual world gradually fades from view
Troxler effect
an unchanging target in peripheral vision will fade and disappear if you steadily fixate a central target
saccade
a type of eye movement, made both voluntarily and involuntarily, in which the eyes rapidly change fixation from one object or location to another
smooth pursuit
a type of voluntary eye movement in which the eyes move smoothly to follow a moving object
superior colliculus
a structure in the midbrain that is important in iniation and guiding eye movement
microsaccade
an involuntary, small, jerky eye movement; important for very fine spatial judgments
reflexive eye movement
a movement of the eye that is automatic and involuntary
optokinetic nystagmus (OKN)
a reflexive eye movement in which the eyes will involuntarily track a continually moving object
three types of eye movements over which we have at least some level of voluntary control
- smooth pursuit movements
- vergence
- saccade
vergence
a type of eye movement in which the two eyes move in opposite directions (convergence or divergence)
saccadic suppression
the reduction of visual sensitivity that occurs when we make saccadic eye movements; eliminates the smear from retinal image motion during an eye movement; when we made a saccade, the visual system essentially shuts down for the duration of the eye movement
efference copy/corollary discharge signal
the phenomenon in which outgoing (efferent) signals from the motor cortex are copied as they exit the brain and are rerouted to other areas in the sensory cortices
comparator
an area of the visual system that receives one copy of the command issued by the motor system when the eyes move (the other copy goes to the eye muscles); compares the image motion signal with the eye motion signal and can compensate for the image changes caused by the eye movement
aspects of motion perception evident at birth
- reflexive eye movements to moving targets
- neurons in V1 have adult-like sensitivity to motion direction
sensitivity to global motion reaches maturity at about…
3-4 years of age
divided attention
splitting attention between two different stimuli
sustained attention
continuously monitoring some stimulus
visual search includes…
attending space, attending time
zoom lens
magnification tool; inversely proportional to field
- large region = less detail (groups as whole)
- small region = more detail (actual individual entities)
limited capacity parallel process
search all objects at once, resources are thinned, sensory memory is limited
attentive stage
- conscious effort
- complex objects
- serial processing (one by one)
stages of feature integration theory
preattentive and attentive
subject-relative change
motion perception based on changes observed relative to the observer’s own frame of reference
object-relative change
motion perception based on changes observed relative to another object or reference point in the environment
two types of motion thresholds
subject-relative change and object-relative change
two types of measurement for motion thresholds
velocity threshold and displacement threshold
velocity threshold
minimum speed or rate of change in position that is required for an observer to perceive motion
displacement threshold
minimum distance that an object must move for an observer to detect the motion
motion perception and retinal eccentricity
- detection of motion higher in periphery
- results in poor image quality
biological systems of motion perception
image-retina system and eye-head system
image-retina system
- responds to changes in image
- image drags across retina
eye-head system
- responds to eye/head movement
- image remains constant on retina
- eye or head moves to track target
stroboscopic movement
- also known as phi movement
- apparent movement
- object appears in two points –> appears to move when nothing moved
- apparent movement influenced by luminance, distance, and tiime
two types of eye-head system
ocular pursuit (reflex pursuit movement) and optokinetic reflex
ocular pursuit (reflex pursuit movement)
smooth pursuit eye movement, a voluntary and predictive mechanism that involves tracking a moving object with the eyes to maintain foveal (central) fixation on the object
optokinetic reflex
involuntary and reflexive mechanism that involves the coordinated movement of the eyes in response to large-field visual motion
voluntary eye movements
- smooth-pursuit movements (convergence and divergence)
- saccades
Aubert-Fleischl Effect
tendency for a moving stimulus to appear to move more slowly when the eyes track it with smooth eye movements than when the gaze is fixated on the static background
optic array
the collection of light rays that interact with objects in the world that are in front of a viewer; some of these rays strike our retinas, enabling us to see
