• Evidence is presented that even early entrances to the brain (the V1 system) are deeply influenced by the constructive predictions coming top down (not just the bottom up senses).

  • The VWFA area of the brain is activated during regular reading in normal subjects and braille reading in blind subjects. Multimodal areas like this make sense in a hierarchical brain where top-down predictions drive perception.

  • Our responses to missing stimuli (e.g. a song missing a particular beat) also suggest the use of generative models in the brain. We habituate to sensory input, but then the removal of the input triggers a surprise response.

  • Gives an example of listening to a familiar song through a bad radio. You know the song but you can also focus attention and hear the bad quality of the radio (turn up the gain on the prediction error).

  • Evidence that perception can occur faster to well-predicted stimuli. Once the top-down model is in accord with the sensory input, perception occurs (and this happens faster with well-predicted stimuli).

  • The generative nature of our top-down models can be repurposed for imagination (endogenous generation of sensory-like states). Perception co-emerges and is a dual of imagination.

  • Reddy et al. experiment where brain signals were recorded as subjects viewed an image and as subjects imagined an image. Classifiers were trained on both sets of data. Classifiers were successful at picking out the images. Classifiers could also be swapped (i.e. the viewing classifier worked for the imagining data). This suggests that the same pathways are activating by viewing and imagining.

  • Evidence is presented that neurotransmitter balance determines how heavily we weight prediction error and thus how much of our modeling is constrained by sensory input vs in a hallucinating/dream state.

  • Argument that sleep is used to regularize/prune overly complex and overfit generative models.

  • PIMMS (predictive interactive multi-memory system): episodic (recalling specific times and place), semantic (knowing what something is), perceptual (recalling specific sensory percepts).