Week 2-3 Illusions & Neuroimaging Flashcards
What is binocular overlap and when do blindspots occur?
We have binocular overlap by having two eyes which enhances our depth perception
Blind spots occur at angles where the light falls where the optic tract leaves the eye / no photoreceptors (the image is project onto the retina but no rods and cones receive it)
When does neural adaptation occur and why?
Visual processing doesn’t do a point-by-point representation, it extracts contours, which are changes in luminance
Neural adaptation is increasing the sensitivity to detect a change if/when it occurs - If the image doesn’t change over time, the brain stops processing, which is modulated attention
Why does neon spreading occur?
Since the colour system has worse spatial resolution than the luminance system, and colours are being filled in with gaps that would complete a rational picture or shape
The density of cells limits how fine detail you can resolve
Why do Stimulus-contrast illusions
occur? (greys looking different shades against a background)
The brain enhances the perceived differences from the foreground and background so they appear more salient and distinctive to compare different objects more clearly - resulting in the same colour appearing as a different shade against different backgrounds
What are metamers?
When physically distinct colours can appear to look identical (red and green light, monochromatic light on a single wavelength = both look identically yellow in colour), the brain perceives things the same
Addictive are metamers (shining light together) and subjective (mixing colours together)
What are bistable percepts? (figure-ground segmentation)
- Bouncing between two precepts by interpreting what is the background and what is the foreground because there are two possibilities
- People study bistables to understand regions of consciousness and what is one’s dominant percept
- Sensory input may determine this, ie. squinting eyes gets rid of finer detail and may see more prominent features of the ‘older woman’ percept
- Flickering between occurs when the brain is unable to decide on a dominant percept (Necker Cube illusion) or interact with each other in unstable percepts
What is the size constancy illusion?
The further away its estimated to be, the bigger its perceived
The full moon near the horizon looks a lot bigger than when it is high up in the sky (perceptual constancy failure)
What are the 2 advantages of single cell recording?
- High temporal resolution
- Tells us how each specific cell is responding to a stimulus
What are the 5 disadvantages of single cell recording?
- Highly invasive (do not do this on humans - only primates)
- The cell will die after it has been inserted with a microelectrode
- Cannot record for long periods of time as the cell is dying
- Cannot measure networks of cells at the same time and population responses
- Biassed towards large single-cell bodies for easier procedures, eg. m cells are more more researched and understood compared to smaller p and koniocellular cells
What are advantages of EEGS and ERPS?
- Good for measuring current brain activity (high temporal resolution)
- Studying states of consciousness
- Can detect and isolate specific regions of seizures
ERPS
- good for studying reactions to specific stimuli and processing stages
-need many trials to avoid cerebral noise
such as 170 ms of stimulus, facial recognition occurs (N170), face identification after 250ms (N250), the ‘N’ stages for negative voltage
P400-600 is time it takes to link a name to a familiar face
What is a study example that uses an ERP?
Hypothesis - Greater attentional engagement with emotional stimuli compared to neutral stimuli and alter the N170/ whether faces are unique
Measurement: motion induced blindness paradigm
- Claim different components of the ERP profile as indicators for early or later attentional processes, ie.
(ERP markers, N2/N200 = early AP.
P3B = late AP). - Understand what ERP neural component to look for and link it to the relevant cognitive process of interest
Are neuroimaging studies more objective than behavioural ones and why not?
- ERPs are not more objective than behavioural studies, because you’re making the assumption that the ERP component is indicative/correlated with the cognitive process of interest, which is a subject interpretation
Eg. The N2/N200 waveform has been claimed to be linked with several different processes, including early attention, executive function and response inhibition.
- Rather in behavioural studies, you need to effectively operationalise your theoretical question and make sure the behavioural task is actually measuring that.
How to determine whether emotional stimuli uses early or late processes?
Test multiple lags in the emotional induced blindness paradigm and compare the time “course of recovery for the emotionally salient stimulus compared to the neutral one” using specific ERP components identified as markers of early or late processing
How are the AB and EIB paradigm similar in lag results?
In the AB paradigm, the second of two targets is usually lost in iconic memory and is harder to detect when it appears close in proximity to the first)
Similarly, the EIB effect occurs when the first target is attentionally affected after a negative valence/positive valence emotive distractor is in closer proximity to the target.
The attentional blindness of both of these paradigms occurs when the 1st target or emotional stimuli closely proceeds the critical target in lags 2-3
Why is neuroimaging often paired with behavioural studies?
- It can imply implicit processing has occurred
- It is a continuous measure to measure multiple stages of processing
