the primate visual systemhelmuth radrich, 24.06.2004 the primate visual system 1.structure of the...

The primate visual system Helmuth Radrich, 24.06.2004

The primate visual system

1. Structure of the eye

2. Neural responses to light

3. Brightness perception & visual acuity

4. Spatial frequency analysis & spatial context

5. Form perception (psychological)

6. Visual pathways & visual cortex (humans)

7. Visual System & form perception (macaque)


Visible spectrum


The crystalline lens


The fovea


Rods and cones distribution


Information flow from eye to brain

• Via optic nerve• Data is not “raw”… preprocessed by retina• Human eye:

– 120 million rods– 5 million cones– Another few millions of bipolar/amacrine/horizontal cells– Optic nerver: 1 million axons

=> A single ganglion cell axon receives information from many receptors in a region of the retina defining the cells receptive field


Neural response types


Receptive fields


Parvo and magno cells


Intensity & perceived brightness


Dark adaptation


Relative sensitivity (wavelength)


Visual angle


Visual acuity






4. Spatial frequency analysis&spatial context





Light distributions


Approximation of square waves


Apparent brightness


Modulation transfer function


Frequency analysis (biological)


Spatial context (lat. inhibition)


Temporal context effects


Properties of visual environment


Masking


Feature extraction


Emergent features


Figure and ground


Subjective contours


Figural grouping


Texture defined grouping


Spatial frequency grouping


Good figures


What is this???


Conceptually driven processing


Global vs. local processing


Context and identification


Receptive fields (simple cortical)


Layer of V1


Visual pathways (human)









7. Visual System & form perception (macaque monkey)


Oram&Prett proposal

• Neurobiological data form macaque monkeys

• Analogies to human visual system

Object recognition as series of 4 computational stages in 7 major hierarchically arranged processing areas

Simple feed-forward network sufficient for computer simulation


• like in humans two major processing streams (only form perception is discussed)

• strong similarities to human brain

• Interconnection not as complete as it could be

Why????

Combinatorial explosion if object is to be recognized from simple features (only edges, etc.)

Basic edges etc. information not helpful in complex feature recognition at higher level


Min.-timings in information-stream

Assumptions (biologically plausible):

• about 5 ms to trigger firing in the next neuron + some ms for signal transmission inside neurons (minimum)

With the experimentally measured timings for the arrival of the first reactions in STPa after stimulus presentation (above):

Only 7 interneuron connections can lay on the way of the signal (correspond to biological layers of the visual cortex)

No time for lateral inhibition or feedback processes to interact with the information processing

Feed-forward only model is plausible, but only half of the story in higher perception


Reference

• Coren, S., Ward, L. M. and Enns, J. T. (1993). Sensation and perception

• Oram M. W. and Prrett, D. I. (1994), Modeling visual cognition from neurobiological constraints. Neural Networks 7 (6/7), 945-972


The END

Thank you for your attention!

the primate visual systemhelmuth radrich, 24.06.2004 the primate visual system 1.structure of the...

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