Work David Marr (neuroscientist)

1 work

1.1 theories of cerebellum, hippocampus, , neocortex
1.2 levels of analysis
1.3 stages of vision

work
theories of cerebellum, hippocampus, , neocortex

marr best known work on vision, before began work on topic published 3 seminal papers proposing computational theories of cerebellum (in 1969), neocortex (in 1970), , hippocampus (in 1971). each of papers presented important new ideas continue influence modern theoretical thinking.

the cerebellum theory motivated 2 unique features of cerebellar anatomy: (1) cerebellum contains vast numbers of tiny granule cells, each receiving few inputs mossy fibers ; (2) purkinje cells in cerebellar cortex each receive tens of thousands of inputs parallel fibers , 1 input single climbing fiber , extremely strong. marr proposed granule cells encode combinations of mossy fibre inputs, , climbing fibres carry teaching signal instructs purkinje cell targets modify strength of synaptic connections parallel fibres. neither of ideas universally accepted, both form essential elements of viable modern theories .

the theory of neocortex motivated discoveries of david hubel , torsten wiesel, found several types of feature detectors in primary visual area of cortex. marr proposed, generalising on observation, cells in neocortex flexible categorizers—that is, learn statistical structure of input patterns , become sensitive combinations repeated.

the theory of hippocampus (which marr called archicortex ) motivated discovery william scoville , brenda milner destruction of hippocampus produced amnesia memories of new or recent events left intact memories of events had occurred years earlier. marr called theory simple memory : basic idea hippocampus rapidly form memory traces of simple type strengthening connections between neurons. remarkably, marr s paper preceded 2 years paper tim bliss , terje lømo provided first clear report of long-term potentiation in hippocampus, type of synaptic plasticity similar marr hypothesized. (marr s paper contains footnote mentioning preliminary report of discovery.) details of marr s theory no longer of great value because of errors in understanding of hippocampal anatomy, basic concept of hippocampus temporary memory system remains in number of modern theories. @ end of paper marr promised follow-up paper on relations between hippocampus , neocortex, no such paper ever appeared.

levels of analysis

marr treated vision information processing system. put forth (in concert tomaso poggio) idea 1 must understand information processing systems @ 3 distinct, complementary levels of analysis. idea known in cognitive science marr s tri-level hypothesis:

computational level: system (e.g.: problems solve or overcome) , similarly, why these things
algorithmic/representational level: how system does, specifically, representations use , processes employ build , manipulate representations
implementational/physical level: how system physically realised (in case of biological vision, neural structures , neuronal activities implement visual system)

after thirty years of vision (1982, w. h. freeman , company), tomaso poggio adds 1 higher level beyond computational level, learning.

i not sure marr agree, tempted add learning top level of understanding, above computational level. [...] may able build intelligent machines learn see—and think—without need programmed it.

stages of vision

marr described vision proceeding two-dimensional visual array (on retina) three-dimensional description of world output. stages of vision include:

a primal sketch of scene, based on feature extraction of fundamental components of scene, including edges, regions, etc. note similarity in concept pencil sketch drawn artist impression.
a 2.5d sketch of scene, textures acknowledged, etc. note similarity in concept stage in drawing artist highlights or shades areas of scene, provide depth.
a 3 d model, scene visualised in continuous, 3-dimensional map.

2.5d sketch related stereopsis, optic flow, , motion parallax. 2.5d sketch represents in reality not see of our surroundings construct viewer-centered 3 dimensional view of our environment. 2.5d sketch paraline drawing , referred generic term axonometric or isometric drawing , used modern architects , designers.