PSYC 325 Lecture Notes - Lecture 9: Perceptual Learning, Weather Forecasting, Electrodermal Activity
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27 Nov 2020
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Week 9 Lecture Notes
March 5, 2020
Medical Example – The pitfalls of overgeneralization
• 90% accuracy in diagnosing a disease of 1% incidence
o 1 in 100 would have it
• 90% accuracy is NOT 100% accuracy
• 100 people @ 1% incidences
• Probably will find the 1 person who has it (.9 probability)
• 90% accuracy in detecting those who don’t have it – means 10% will be diagnosed
falsely
• 99 people who don’t have it X 10% = 9.9 people falsely diagnosed to one properly
diagnosed
• Only 1 in 11 diagnoses is true
Generalization and Discrimination Learning – Chapter 6
• Behavioral processes
• Brain substrates
• Clinical perspectives
Brain Substrates: Review from Chapter 3 (Perceptual Learning)
• Perceptual learning (learning to better process a stimulus) involves complex changes in
brain function:
– Refinement of neuronal receptive fields
– Changes in overall cortical representations (alterations in cortical maps)
• Similar cortical re-organization occurs during generalization and discrimination
behaviors.
Cortical Representations of Sensory Stimuli
•
•
(e.g., homunculus for touch).
• This topography occurs via adjacent
cells with overlapping receptive
fields.
Initial cortical processing of sensory information occurs in
areas dedicated to each sense.
Each area exhibits an anatomical mapping of the sense
Distributed Representations and Neurons
• Neuron receptive fields are tuned “broadly” - responses are graded.
• Shape of the response curve is similar to that of the generalization gradients observed
in behavior
Distributed Representations and Neurons
Distributed Representations and Neurons
•
Discrimination training only alters receptive fields if
the input is
meaningful.
–
E.g., tone predicts food or shock
–
No altered fields with mere exposure
•
Consistent with this, destruction of primary auditory
cortex eliminates ability to discriminate between tones.
•
Thus, experience shapes the distributed cortical
representations of sensory inputs.
Distributed Representations and Neurons
• As experience shapes receptive fields, the topography of the cortex is also
reshaped:
– Habituation to a tone: contracts cortical space devoted to that pitch
– Fear conditioning to a tone: expands cortical space devoted to that pitch
Generalization and the Hippocampal Region
• The hippocampus plays an important role in learning about relationships between
sensory cues.
• Specifically, hippocampus damage disrupts performance in:
– Sensory preconditioning tasks
– Acquired-equivalence tasks
– Latent inhibition
• The hippocampus seems to be active early in training, and then its role declines.
– Facilitates learning about relationships between stimuli (relational learning).
Generalization and the Hippocampal Region – Example
• Phase 1: Two stimuli (tone + light) are paired together.
• Phase 2: One of the two stimuli becomes a CS (light → airpuff).
• Phase 3: Another stimulus that is presented (tone) should evoke CR (generalization).
• Animals exposed to the stimuli separately don’t generalize.