LEARNING & MEMORY Jaan Aru [email protected]
Deep neural nets Learning through weight changes
Feedback connections! But the biggest difference?
The most famous patient: H.M. Hippocampus Medial temporal lobe
Patient H.M. Types of memory
MEMENTO Patient H.M. demonstrates that ...
1) medial temporal lobe is important for memory 2) but it is not necessary for all memory! 3) there is a difference between short-term and long term memory
4) there is a difference between declarative and procedural memory 5) medial temporal lobe is necessary for long term declarative memory
Taxonomy of long-term memory complementary learning systems (CLS)
intelligent agents must possess two learning systems neocortex and hippocampus (MTL) NC gradually acquires structured knowledge
HC quickly learns the specifics of individual experiences. Structured Knowledge
Representation System in Neocortex hippocampus Instance-Based Representation in the
Hippocampal System pattern separation: DG is crucial in selecting a distinct neural activity pattern in CA3 for each experience pattern completion : in CA3 reactivation of part of the pattern that was
activated during storage can reactivate the rest of the pattern Open question What constitutes an individual experience?
= when does hippocampus do its dance? Every moment something changes .. New experience whenever a big change in high level semantic features
Replay of Hippocampal Memories Replay of Hippocampal Memories
Circumventing the Statistics of the Environment All the experiences dont have the same priority! 1. Experience can have different lengths 2. replay is biased towards rewarding events
Novel, significant reweighting experiences shapes neocortical learning For the cortex it is the same
One shot learning? Can we apply it in AI??
DeepMind: experience replay
interleaved with ongoing game-play
biasing replay towards significant events
Prioritized experience replay
Its success supports the role of the hippocampus in reweighting experiences
external memory differentiable neural computer
Taxonomy of long-term memory ENCODING
RETRIEVAL CONSOLIDATION
ENCODING But what are these stored features? What gets actually stored?
One image, hundred ways to encode it How you encode it determines how you remember
ENCODING CONSOLIDATION
RETRIEVAL For remembering, try to
go mentally back to the situation where you learned it
Encoding what? What you encode determines what you remember! What you encode depends on your mood, attention, other thoughts and associations it is highly variable
Adult humans mostly do not encode sensory features, but rather semantic concepts Transfer learning is hard with sensory features, but easy with semantic concepts
Transfer learning Transfer learning is as good as your features Transfer learning is hard with sensory features, but
easy with semantic features As two similar things might be very different in sensory space Whereas semantic features are multisensory /
amodal different sensory features can be combined Summary
ANNs learn structured knowledge Learning single experiences is essential Based on hippocampus Prioritized replay to cortex
Applying in AI has been a success (DeepMind) One image, hundred ways to encode it Semantic encoding enables transfer
