M2 Lecture 12: Feb 21 Flashcards
what is Apparent motion:
The illusory impression of smooth motion resulting from the rapid alternation of objects that appear in different locations in rapid succession.
explain Motion detection circuit
- M neuron registers a change in position between A and B.
- Add neuron D which incorporates delay
- Repeat this across many X comparator neurons
explain the the What pathway has what kind of cells
P ganglion cells receive inputs from midget bipolar cells (1 cone per midget cell). P cells project to the parvocellular layers of the LGN.
P ganglion cells have small receptive fields. The high-resolution information coming from these P cells is at the origings of the ventral «what» pathway
explain the where pathway
M ganglion cells receive inputs from diffuse bipolar cells (>1 cone per diffuse cell). M cells project to the magnocellular layers of the LGN.
M ganglion cells have large receptive fields and are sensitive to movement
what is the Correspondance problem:
The problem faced by the motion detection system of knowing which feature in frame 2 corresponds to which feature in frame 1.
what is the Aperture problem:
The fact that when a moving object is viewed through an aperture (or a receptive field), the direction of motion of a local feature or part of an object may be ambiguous.
what are apertures
receptive fields
Motion information from several local apertures (or receptive fields) can be combined to determine what
the global motion of the object.
There are several directions of motion within each aperture that are compatible with the stimulation the receptor is receiving
how to determine the true global motion direction of the object.
Whichever possible motion direction is the same in all apertures is the true global motion direction of the object.
Lesions in magnocellular layers of LGN impair what
perception of large, rapidly moving objects
Monkeys needed____ times as many dots to correctly identify direction of motion
about ten
what also plays an important role in motion perception
Middle temporal area (MT)
what is Motion aftereffect (MAE):
The illusion of motion of a stationary object that occurs after prolonged exposure to a moving object
Existence of MAE implies what
an opponent process system, like that of color vision
what is Interocular transfer:
The transfer of an effect (such as adaptation) from one eye to another
explain Interocular transfer and how it relates to MAE
MAE exhibits interocular transfer.
- > Therefore, MAE must occur in neurons that respond to both eyes. - > Input from both eyes is combined in area V1, so MAE must be in V1 or later. - > Recent studies with fMRI confirm that adaptation in MT is responsible for MAE.
whats First-order motion:
The motion of an object that is defined by changes in luminance
what is Luminance-defined object:
An object that is delineated by differences in reflected light.
what is Second-order motion:
The motion of an object that is defined by changes in contrast or texture, but not by luminance
what is Texture-defined (contrast-defined) object: (second order motion)
An object that is defined by changes in contrast or texture, but not by luminance.
Indicates that the visual system does not simply track objects’ positions over time to calculate movement, as this display demonstrates (since there are no objects to track!).
is seeing passive
no
Why do we perceive the finger to be in motion in the first case, but perceive the fixation point to be stationary in the second case? After all, both items moved across our retinas to the left.
-> Because in the second case there was an eye movement
what are the Types of eye movements
smooth pursuit saccade vergence Reflexive eye movements: Microsaccade
what is Smooth pursuit:
Voluntary eye movement in which the eyes move smoothly to follow a moving object.
what is 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 (3-4 seconds every second).
what is Vergence:
A type of eye movement, both voluntary and involuntary, in which the two eyes move in opposite directions.
give the two types of Vergence
Convergent eye movements turn the eyes inward
Divergent eye movements turn the eyes outward.
what is Reflexive eye movements:
automatic and involuntary eye movements.
what isMicrosaccade
an involuntary small jerklike eye movement.
what is the purpose of Microsaccade
- prevent visual fading
- allowing us to see behind the blood vessels in our eye
- improve visibility of sharp details
- compensate for the sudden loss of acuity a few minutes outside of the fovea
when the eyes move to compensate for head and body movement while maintaining fixation on a particular target.
this is an example of what
Reflexive eye movements
what is the Control of eye movements
Controlled by an extensive network of structures in the brain
Superior colliculus
Frontal eye field
Saccadic suppression:
Comparator
Six muscles are attached to each eye and are arranged in three pairs
what does the Superior colliculus do
A structure in the midbrain that is important in initiating and guiding eye movements.
do all the neurons in the SC produce the same eye movements
Different neurons in the SC produce different eye movements (e.g., left, up, etc.)
what is the Frontal eye field
A structure in the frontal lobe that is important in initiating and guiding eye movements
Different neurons in the FEF will do what
move the eye to different spots in space (irrespective of the actual movement required
what is Saccadic suppression
The reduction of visual sensitivity that occurs when we make saccadic eye movements.
Saccadic suppression eliminates what
the smear from retinal image motion during an eye movement.
- > Ex.: move your eye voluntarily vs by pushing it with your finger (close the other eye).
- > Ex.: look at yourself in the miror, fix an eye, then the other, you don’t notice your eyes moving.
what is the Comparator:
An area of the visual system that receives one copy of the order issued by the motor system when the eyes move (the other copy goes to the eye muscles).
The comparator can do what
compensate for the image changes caused by the eye movement.
explain the process of Dynamic remapping of receptive fields
- A saccade is planned but not yet executed.
- Some neurons in parietal cortex remap their receptive fields relative to upcoming fixation location.
- Saccade is executed.
4. Receptive fields are already processing information from new location before eye lands there.
What are these receptive fields ?
(in dynamic remapping)
- Eyes are fixated on the fixation point
- Recording from a neuron in the intraparietal region.
- The neuron fires only if something is presented in the red circle.
- Hence, the red circle is the receptive field of that neuron.
Receptive fields of neurons in the frontal eye fields also transiently shift where
inward towards the new point of fixation.
what is Inattentional blindness:
A failure to notice—or at least to report—a stimulus that would be easily reportable if it were attended.
what are the types of attention
selective divided sustained external internal overt covert
what is Attention:
Any of the very large set of selective processes in the brain.
what is Selective attention:
The form of attention involved when processing is restricted to a subset of the possible stimuli.
what isDivided attention:
Splitting attention between two different stimuli
what is Sustained attention:
Continuously monitoring some stimulus
what s External attention:
Attending to stimuli in the world
what is Internal attention :
Attending to one line of thought over another or selecting one response over another
what is Overt attention
Directing a sense organ toward a stimulus, like turning your eyes or your head
what is Covert attention
Attending without giving an outward sign you are doing so
what model explains Selective attention
broadbent’s filter model
what is Attentional Bottleneck:
Getting the stimulus from sensory processes to memory processes requires attention.
what is Spotlight” model of attention:
Attention is restricted in space and moves from one point to the next. Areas within the spotlight receive extra processing.
what are the two categories of Spotlight” model of attention:
Top-down (endogenous) control: Bottom-up (exogenous) control:
what is Top-down (endogenous) control:
attention is voluntarily directed towards stimuli relevant to current goals
what is Bottom-up (exogenous) control
attention is involuntarily captured by things that «stand out».
what is Cue:
A stimulus that might indicate where (or what) a subsequent stimulus will be
what can a cue be
Cues can be valid (correct information), invalid (incorrect), or neutral (uninformative)
explain Cueing as a tool for examining attention
Simple probe detection experiment -Posner cueing paradigm Cues can be valid or invalid -RTs are shorter on valid cue trials -RTs are longer on invalid cue trials
what is Exogenous/peripheral cue:
In directing attention, an exogenous cue is located out (exo) at the desired final location of attention.
what is Endogenous/symbolic cue:
In directing attention, an endogenous cue is located in (endo) or near the current location of attention
