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 Lecture 4: Coding in the Nervous System 2

Content Definition: Knowledege of a Code Experiments: Rate Codes Experiments: Temporal Codes Coding Categories Overview Weekly Questions Lecture 4: Coding in the Nervous System 3

Definition: Code A code is simply a function from one signal domain onto another. Lecture 4: Coding in the Nervous System 4

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 outputs from a system by observing an internal signal or vice versa. Lecture 4: Coding in the Nervous System 5

Definition: information on a Code (2/2) An even less stringent requirement: we do have knowledge of 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. Lecture 4: Coding in the Nervous System 6

Content Definition: Knowledege of a Code Experiments: Rate Codes Experiments: Temporal Codes Coding Categories Overview Weekly Questions Lecture 4: Coding in the Nervous System 7

Muscle Output Static Charges make Frog Legs Twich (Galvani 1780) Lecture 4: Coding in the Nervous System 8

Rate Response of Orientation Selective Cells in V1 (Hubel and Wiesel) Lecture 4: Coding in the Nervous System 9

Segmentation by Synchrony Lecture 4: Coding in the Nervous System 10

Content Definition: Knowledege of a Code Experiments: Rate Codes Experiments: Temporal Codes Coding Categories Overview Weekly Questions Lecture 4: Coding in the Nervous System 11

Precise Spike Patterns as Response to High Entropy Stimuli (Bair and Koch) Lecture 4: Coding in the Nervous System 12

Synfire Chains (Abeles) Lecture 4: Coding in the Nervous System 13

Phase Shift in Hippocampal Place Cells (O’Keefe and Recce) Lecture 4: Coding in the Nervous System 14

Spike Timing Dependent Plasticity, Spike Based Learning Lecture 4: Coding in the Nervous System 15

Reaction Time In Psychophysical Recognition Tasks (Simon Thorpe) (1/2) 150ms to 200ms reaction time in visual recognition task Lecture 4: Coding in the Nervous System 16

Reaction Time In Psychophysical Recognition Tasks (Simon Thorpe) (2/2) Lecture 4: Coding in the Nervous System 17

Content Definition: Knowledege of a Code Experiments: Rate Codes Experiments: Temporal Codes Coding Categories Overview Weekly Questions Lecture 4: Coding in the Nervous System 18

Coding Categories Overview Lecture 4: Coding in the Nervous System 19

Example Coding-Function: Latency Encoding Lecture 4: Coding in the Nervous System 20

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? Lecture 4: Coding in the Nervous System 21