1. Memory and Cognition PSY 324 Chapter 2: Cognition and the Brain Part III: Neural Representation Dr. Ellen Campana Arizona State University

2. What is representation? A representation is something that “stands for” something else A representation is something that “stands for” something else Neural representation of perception of a tree is not the same thing as the tree itself Neural representation of perception of a tree is not the same thing as the tree itself Everything we see, hear, do, smell, remember, taste, touch, pay attention to, and think about is represented physiologically by neurons firing Everything we see, hear, do, smell, remember, taste, touch, pay attention to, and think about is represented physiologically by neurons firing All sensations, perceptions, memories and thoughts are represented by neural activation All sensations, perceptions, memories and thoughts are represented by neural activation

3. Hubel & Weisel Single-cell recording of feature detectors Single-cell recording of feature detectors Simple neurons (from the video last time) Simple neurons (from the video last time) Orientation (thickness, location of line) Orientation (thickness, location of line) Complex neurons Complex neurons Orientation, direction of motion Orientation, direction of motion End-stopped End-stopped Length, direction of motion Length, direction of motion

4. Feature Detectors Lines (shapes and orientations) Lines (shapes and orientations) Directed Motion Directed Motion Complex Stimuli Complex Stimuli Geometrical figures Geometrical figures Common objects in the environment (houses, man- made objects, birds) Common objects in the environment (houses, man- made objects, birds) Faces Faces Depend on selectivity – neurons firing at some times and not at others Depend on selectivity – neurons firing at some times and not at others

5. Neural Codes in Daily Life Consider the case of recognizing the face of a specific person – how could that happen? Consider the case of recognizing the face of a specific person – how could that happen? Hypothesis 1: specificity tuning – a particular neuron could selectively fire when you see that person Hypothesis 1: specificity tuning – a particular neuron could selectively fire when you see that person

6. Specificity Coding Difficulties with Specificity Coding Hypothesis Difficulties with Specificity Coding Hypothesis Too many different faces, concepts, etc. to have a neuron for each one Too many different faces, concepts, etc. to have a neuron for each one Depends on experience – would have to learn each face (because neurons don’t reproduce) Depends on experience – would have to learn each face (because neurons don’t reproduce) Neurons selective for faces are active for many different faces Neurons selective for faces are active for many different faces Related idea: Grandmother cell (coined by Lettvin) Related idea: Grandmother cell (coined by Lettvin) Cell responds to image of a grandmother, general concept of grandmothers, your own grandmother Cell responds to image of a grandmother, general concept of grandmothers, your own grandmother Some evidence that these might exist in Hippocampus – associated with memory storage, not vision Some evidence that these might exist in Hippocampus – associated with memory storage, not vision For recognition (and many other types of cognition), specificity coding is not enough For recognition (and many other types of cognition), specificity coding is not enough

7. Neural Codes in Daily Life Hypothesis 2: Distibuted Coding – code for a specific face is distributed across a set of neurons Hypothesis 2: Distibuted Coding – code for a specific face is distributed across a set of neurons

8. Distributed Coding Advantages Advantages Efficient -- firing of fewer neurons can represent many more different stimuli Efficient -- firing of fewer neurons can represent many more different stimuli Similar items can have similar neural codes Similar items can have similar neural codes Helps with learning Helps with learning Graceful degradation -- if one or two neurons do not fire for some reason, it is still possible to recognize that person’s face Graceful degradation -- if one or two neurons do not fire for some reason, it is still possible to recognize that person’s face

9. Reconciling types of coding Evidence for Specificity Coding Evidence for Specificity Coding Feature detectors Feature detectors Concept cells in hippocampus (memory area) Concept cells in hippocampus (memory area) Argument for Distributed Coding in recognition Argument for Distributed Coding in recognition Clear theoretical advantages in recognition Clear theoretical advantages in recognition Will see a lot of evidence later Will see a lot of evidence later Both are happening in the brain – in different areas at the same time (parallel processing) Both are happening in the brain – in different areas at the same time (parallel processing) Pattern across (+ interaction btwn) areas=cognition Pattern across (+ interaction btwn) areas=cognition

10. The End Chapter 3 is next! Chapter 3 is next!