Lecture 4 Cortex and Beyond Flashcards
What is center-surround antagonism?
intermediate responses when both inhibitory and excitatory regions of a visual center-surround receptive field is stimulated
Describe the visual pathway.
- optic nerve
- LGN
- V1 (striate cortex)
- temporal/parietal lobe (dorsal/ventral streams)
- frontal lobe
What is the role of the superior colliculus in the visual pathway? What percentage of the nerve fiberes leaving the eye does it account for?
control eye movements’ 10%
What is the role of the LGN in the visual pathway? What percentage of the nerve fibers leaving the eye does it account for?
- center-surround receptive fields (like in the retina)
- may regulate or filter info passed along to V1
- 90%
Describe the feedback mechanism of the LGN in the visual pathway.
- LGN receives more info FROM the cortex than it sends to the cortex
What are feature detectors?
neurons that fire in response to specific features of a stimulus
TRUE or FALSE: receptive fields of neurons in the visual cortex are centre-surround
FALSE: feature detectors
What are the major types of feature detectors in V1?
- simple
- complex
- end-stopped
What are orientation tuning curves?
they plot the response of a simple cortical cell to line stimuli of varying orientations
What are the characterisitcs of the simple cortical cell?
- excitatory and inhibitory areas arranged side-by side
- responds best to bars of a particular ORIENTATION
What are the characteristics of the complex cortical cell?
- response best to MOVEMENT of a correctly ORIENTED bar across the receptive field
What are the characteristics of an end-stopped cortical cell?
responds to corners, angles, or bars of a particular LENGTH moving in a particular DIRECTION
What is the absolute threshold?
smallest amount of energy needed to detect a stimulus
What can be used to determine the absolute threshold?
Method of Limits
What is the Method of Limits used to determine? What are the steps?
- determine absolute threshold
1. present stimuli of different intensities in ascending and descending order
2. record whether the stimulus can be perceived in each trial
3. average the cross-over point
What is selective adaptation?
phenomenon in which neurons tuned to specific stimuli properties fatigue with prolonged exposure to stimuli containing those properties
fatigue or adaptation to stimulus causes a decrease in both:
- baseline firing of those neurons
- the response of those neurons to repeated presentation of the stimuli they have been adapted to
Provide an example of selective adaptation.
feature detectors tuned to respond to vertical lines will fatigue when shown lots of vertical lines, but other feature detectors should be unaffected
What are gratings?
the typical stimuli used for selective adaptation, made of alternating light and dark bars
How are gratings used to test selective adaptation?
- angle relative to vertical can be changed to test for sensitivity to ORIENTATION
- difference in intensity can be changed to test for sensitivity to CONTRAST
What is the general experimental procedure for testing selective adaptation?
- measure sensitivity to range of one stimulus property (baseline); determine contrast THRESHOLD by decreasing intensity of grating until person can just see it, and SENSITIVITY (reciprocal)
- adapt neurons with extended exposures of stimuli that have the property being tested
- remeasure the sensitivity to range of the same stimulus property
Describe the relationship that allows us to make causal claims about how neural activity affects perception.
we can observe a change in perception (contrast threshold) that we have experimentally demonstrated is caused by a change in physiology (selective adaptation)
What is selective rearing?
raising animals in environments that contain only certain types of stimuli (while depriving exposure to other kinds)
Describe Blakemore and Cooper’s 1970 experiment? What did they test?
- assessed selective rearing and how that affects perception
- manipulated whether kittens were raised in environments with (only) either horizontal or vertical lines
- kittens raised in an environment of all vertical lines couldn’t perceive horizontals (and vice versa)
- effects apparent in both behavioural and neural responses
