INF5470 Fall 2012 Lecture 4: Coding in the Nervous System Content - - PowerPoint PPT Presentation

INF5470 — Fall 2012

Lecture 4: Coding in the Nervous System

Content

Definition: Knowledege of a Code Experiments: Rate Codes Experiments: Temporal Codes Coding Categories Overview Weekly Questions

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Content

Definition: Knowledege of a Code Experiments: Rate Codes Experiments: Temporal Codes Coding Categories Overview Weekly Questions

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Definition: Code

A code is simply a function from one signal domain onto another.

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Definition: information on a Code (1/2)

We do have knowledge about a code if we can assign unencoded and encoded signals to each-other for at least a subset of all possible signals. In other words if we can reconstruct some of the inputs to a system by observing internal encoded signals or vice versa, or if we can predict

• utputs from a system by observing an internal signal or

vice versa.

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Definition: information on a Code (2/2)

An even less stringent requirement: we do have knowledge

• f a code even if we can assign unencoded/encoded

signals to members of limited set of encoded/unencoded signals with given probability. I.e. if we can reconstruct a partial input from looking at a output code, in other words limit the possible inputs. Or correspondingly, predict an approximate output from looking at an internal/input signal.

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Content

Definition: Knowledege of a Code Experiments: Rate Codes Experiments: Temporal Codes Coding Categories Overview Weekly Questions

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Muscle Output

Static Charges make Frog Legs Twich (Galvani 1780)

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Rate Response of Orientation Selective Cells in V1 (Hubel and Wiesel)

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Segmentation by Synchrony

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Content

Definition: Knowledege of a Code Experiments: Rate Codes Experiments: Temporal Codes Coding Categories Overview Weekly Questions

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Precise Spike Patterns as Response to High Entropy Stimuli (Bair and Koch)

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Synfire Chains (Abeles)

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Phase Shift in Hippocampal Place Cells (O’Keefe and Recce)

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Spike Timing Dependent Plasticity, Spike Based Learning

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Reaction Time In Psychophysical Recognition Tasks (Simon Thorpe) (1/2)

150ms to 200ms reaction time in visual recognition task

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Reaction Time In Psychophysical Recognition Tasks (Simon Thorpe) (2/2)

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Content

Definition: Knowledege of a Code Experiments: Rate Codes Experiments: Temporal Codes Coding Categories Overview Weekly Questions

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Coding Categories Overview

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Example Coding-Function: Latency Encoding

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Weekly Questions

• 1. How is a reconstruction from a rank order code of a

black and white image impaired? Imagine 2x2 pixels, two of them black, the other two white. What information is lost in the encoding?

• 2. Can you again explain why a rate-, population code

can also lead to overall fast response times and might be an alternative explanation of the Thorpe reaction times experiment?

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