Models and Analogues in Biology

By Society for Experimental Biology | Go to book overview

Plate 1. First, let one eye be closed, and let the observer rotate his open eyeball to and fro by pressing as lightly as possible on the outer corner of the eyelid, while looking at the figure. A curious non-Euclidean distortion of the pattern will be seen ( MacKay, 1958). The rays lying nearest to the direction of displacement of the image appear to diverge and converge as if the figure were on an elastic surface being locally distended and contracted. If, however, a thread or other marker is laid across the direction of image-displacement to one side of the centre, the distortion in its neighbourhood is suppressed, although on the opposite side (without a marker) it persists unaltered. The details of the illusion do not concern us now, and the perceptual process involved is unlikely to lie in the primary visual cortex; it is intended only to illustrate the apparent need for a continuous model, incorporating such features as elasticity.

The final illustration also depends on Plate 1. If the pattern is inspected for about ten sees. in a good light, and then quickly replaced by a blank surface, the latter appears to be traversed briefly by a circular swirl of shadowy, wavy lines whose general direction is roughly perpendicular to the lines of the stimulus figure. By superimposing on Plate 1 a background of random visual 'noise' (a succession of dots in randomly varying positions) it has proved possible to excite perception of what I have called the 'complementary image' continuously--rather in the way that iron-filings reveal the state of strain around a magnet ( MacKay, 1957). Any pattern with more than, say, four to eight roughly parallel lines has been found to generate a neural state of strain, forming a moving complementary image of this sort.

Once again we need not stay now with details. It would seem however that this kind of persistent and powerful long-range interaction, occurring between widely separated areas of the visual field, and independent of position on the retina, bespeaks the type of continuous model we have been discussing, incorporating essentially mobile and wave-like patterns of excitation.


CONCLUSIONS

Can any conclusions be drawn at this stage in a rapidly-moving process? Digital computing mechanisms seem to have had their day as models of complex neural systems, though digital computors used as simulators of more realistic models may well be indispensable as complexity increases. Analogue simulators too--as Taylor ( 1956) and others have shown--are likely to be of increasing value, while circuits that grow and function under statistical feedback should fill an important gap in our model-making repertoire. The only additional suggestion in this paper is that in all such models we seem to be already too near the limits of practicability if we insist on using discrete circuit-elements and discrete connexions. For systems of multi-million (or

____________________
The effect has nothing to do with distortion of the eyeball. It occurs equally strongly if the eye can be held steady and the image displaced by reflexion in a lightly-rocked mirror.

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Models and Analogues in Biology
Table of contents

Table of contents

  • Title Page iii
  • Contents v
  • Preface vii
  • Quantum Physics and Biology† 1
  • Models in Genetics 6
  • Kinetic Models of Development And Heredity 13
  • Tissues in Culture and in the Body 28
  • References 40
  • Models of Muscle 41
  • References 66
  • Mechanical Models in Zoology 69
  • Conclusions 82
  • Physical Models in Biology 83
  • Estimation of Values Of Parameters of a Model to Conform With Observations 102
  • Summary 120
  • Applications of Theoretical Models to the Study of Flight- Behaviour in Locusts and Birds 122
  • References 138
  • Electrical Analogues in Biology 140
  • Computers and the Nervous System 152
  • References 168
  • Models in Cybernetics 169
  • References 190
  • Modelling of Large-Scale Nervous Activity 192
  • Conclusions 197
  • Energy Models of Motivation 199
  • Summary 212
  • The Use of Models in the Teaching Of Embryology 214
  • School Biology as An Educational Model 230
  • Conclusion 241
  • The Problem of Communication In Biological Teaching 243
  • Acknowledge Ments 248
  • A Review of the Symposium: Models and Analogues in Biology 250
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