Lecture 4: Binocular Rivalry and Neural Coding Flashcards
How was binocular rivalry studied in monkeys and what was found?
Binocular rivalry was studied in monkeys who were trained to pull a lever when it sees a particular image, through these studies we found that the images for the monkeys also fluctuates.
How could it be identified what the monkeys were seeing?
Several (6) face selective areas in the inferior temporal cortex (IT) of macaque monkeys could also be used to identify which image they were perceiving. It only fired when the monkeys perceived the face
How did other visual areas in the macaque brain respond to binocular rivalry?
Activation in early areas of the visual stream such as the LGN (<10%), area V1 and V2 (10 - 20%) are barely correlated with the perceptual modulation while later (mainly frontal parietal) areas such as STS, IT, FEF and LPFC (>50%) are more highly correlated with what the person perceived rather than the base visual input.
Describe the results further discovered from this research on facial areas of macaque monkeys (prolly not on exam)
Cells were also found which responded more favourably to images of faces with specific features such as hair or irises. Cells from a more anterior region responded selectively to different people. These areas are purposefully connected and likely form some form of assembly line, generating the percept of a whole face
To what extent can Binocular Rivalry be used to study NCC?
Good for studying spontaneous switches of perception but not optimal for isolating the NCC, because there is no “unconscious condition” to contrast with. Difficult to separate cause and effect (consciousness is not manipulated, treated more as a dependent variable)
Describe the subliminal semantic processing research paradigm
There is a masked and unmasked trial. Subjects were presented with a number first as a prime for 200ms. A second target number was then displayed for 43ms. These numbers could be congruent or incongruent and each could either be in word format (e.g nine) or in arabic format (e.g 9). Subjects had to press with their left hand if the second number was smaller than five, and with their right hand if the number was larger than five.
In the masked condition, masks of 71ms were placed before and after the presentation of the target numbers, containing non-words of random letters. In the unmasked condition, there was a blank screen displayed for these 71ms.
What were the initial results of this semantic processing research study?
The overall response times were slower when the numbers were congruent compared to incongruent. Reaction times were also faster when the target was arabic (probably easier to process).
Give some possible explanations as to why the congruent RT’s were faster
There is motor activation (‘response priming’) in the absence of awareness. So even if we don’t see the prime, we see that people are slower for incongruent than congruent trials.
this is not just driven by “low-level factors (e.g exact repitition) but is semantic in nature (six, 6). This means that the semantic meanings of the words have to be extracted.
What results were found after this study was conducted in an fMRI machine?
Activation was found in the motor cortex. In the left motor cortex there was more activation when people made an overt response (i.e pushed a button) with their right hand as expected. The opposite pattern was also found in the right cortex as expected.
When we contrast the words that are seen vs. nothing, we see activity in the large area of fronto-parietal network brain regions as well as the visual word form area. When we look at the invisible words vs. nothing, this fronto-parietal activation has disappeared, but we still see activity int he visual word form area. The response in the visual word form area is much weaker for unseen words, but it is still present
This demonstrated that there was priming for unconscious stimulus and that unconscious stimulus activates the motor cortex and, depending on the congruency, either increase or decrease the activity in that cortex .
How can you know if the participants doing the forced choice task cannot perceive the stimulus shown?
Forced choice task, It will be about 50/50: they are guessing
Describe a method of determining whether participants can consciously perceive a stimulus which was not used in the dehaene paper
Using sounds: in the fMRI scanner (a lot of noise) faint sounds are made and participants must report whether they heard one or not (sometimes they are, sometimes not.) You then contrast detected sounds vs non-detected sounds in the fMRI.
Similar patterns are shown as unconscious visual stimuli, with activation shown in the auditory cortex but not to the same level as with conscious stimuli and fronto-parietal activity which is observed in conscious but not unconscious sounds.
Note: Consciousness is treated as a dependent variable here (conditions are post hoc determined based on report)
Discern between objective and subjective measurements of ‘conscious’ stimulus material
Objective tasks: manipulate consciousness task performance (detection=Yes/No, discrimination=this or that)
Subjective tasks: report
•“Have you seen/heard/felt the stimulus?” yes/no
•Or more graded versions of perception (1-10 scales for example)
•Confidence scales (1-6)
•Post-decision wagering
Discern between objective and subjective measurements of ‘conscious’ stimulus material
Objective tasks: manipulate consciousness task performance (detection=Yes/No, discrimination=this or that)
Subjective tasks: consciousness in dependent variable
•“Have you seen/heard/felt the stimulus?” yes/no
•Or more graded versions of perception (1-10 scales for example)
•Confidence scales (1-6)
•Post-decision wagering
What four terms are often used to describe responses in signal detection theory
Hit- correctly reported
Miss - incorrectly did not report
False alarm - incorrectly reported
Correct rejection: correctly did not report
What does sensitivity refer to in SDT?
True ability to detect the presence or absence of a signal -Better hearing, higher sensitivity; poorer hearing, lower sensitivity
