3 - Visual processing with and without awareness Flashcards
What is paracontrast?
Forward masking
What is metacontrast?
Backward masking
What is stimulus onset asynchrony (SOA)?
The interval between onset of target and of mask
What is stimulus termination asynchrony (STA)?
The interval between termination of target and of task
What is inter-stimulus interval (ISI)?
The interval between termination of target and onset of mask or between termination of mask and onset of target
What is the best predictor of backward masking?
STA, as dispersion of the peak masking times was lowest when performance was plotted on STA scale. The termination of the mask has the strongest effect on masking.
What is the best predictor of forward masking?
ISI
What is the effect of masking on the neural response?
It inhibits the target response and the after-discharge.
How do you identify a transient neuron?
A transient neuron reacts when a stimulus appears and when a stimulus disappears
How do you identify a sustained neuron?
A sustained neuron keeps firing as long as a stimulus is visible
It is sort of counterintuitive that after-discharge contributes to a target’s visibility as real objects don’t turn off. How does it actually make sense?
Our eyes are rarely stationary so actually, the objects do turn on and off several times per second for the perspective of the receptive field. If this were not the case and we had perfect fixation, everything would just disappear after a short amount of time (fading effect).
What is the dorsal pathway in visual perception?
The dorsal pathway is magno-dominated (fast) and targets the parietal cortex. It is important for spatial information, movement and action.
What is the ventral pathway in visual perception?
The ventral pathway is parvo-dominated (slow) and targets the temporal cortex. It is important for object/source identification.
What are the multiple ways recurrent connections can be incorporated into the response?
- Change in tuning of a neuron overt he course of this response
- Modulation of cell’s response by contextual info occurring its cRF
- Processing times
Explain masking in terms of feedforward sweep and recurrent processing
If the feedforward sweep (which is already processing the mask) and feedback from recurrent processing (which reports back on the target) disagree with each other, the representation of the target gets thrown into the trash as it is no longer useful.
What is the method of Macknik?
HUMAN STUDY
forward and backward masking, subject had to indicate which side had the longer target. Changed the many intervals: SOA, STA, ISI.
MONKEY STUDY
looked what effect masking (that we know was effective based on human studies, both forward and backward on transient and sustained neurons) had on the neuronal responses in V1
How can we based on the performance as function of ISI say that mask termination produces a particularly strong masking effect?
Because the max backward masking is seen at shorter ISI for longer duration masks. Mask and target overlapping because STA is kept constant, this is why ISI goes negative in the ISI graph
As target duration increases, the SOA increases. explain
The SOA = task + ISI. long task and short ISI or short task and long ISI give the same SOA
Why is the claim that Macknik makes in his abstract not fully supported by the data?
ABSTRACT
Macknick claims that forward masking only inhibits the onset and backward masking inhibits the after discharge and therefore both are essential for vision.
DATA
Data show that forward masking inhibits the onset and the after discharge while backward masking only inhibits the after discharge and less so than forward masking. this makes forward masking a more effective masking technique than backward masking and after discharge seems to be more important to the visibility of the stimulus than onset response.
