IV.l The Metabolic Cost of Informationa Fundamental Factor in Visual Ecology
Simon B. Laughlin
Department of Zoology, University of Cambridge, Downing St, Cambridge CB2
3EJ, UK
Abstract
To better understand the adaptations of form to function that constitute much of
contemporary visual ecology, we examine the costs and the benefits associated
with the first stages of vision. Taking the blowfly as a model, the major metabolic
costs are the metabolic energy used to support the mass of the eye during
locomotion and the metabolic energy used to generate electrical signals. These
account for 10% of total metabolic rate at rest, and 3% in flight. This significant
contribution to total metabolic rate helps to explain the numerous adaptations that
maximize the efficiency with which the components of sensory systems capture
and encode information. To further understand these adaptations, metabolic costs
are related to sensory benefit by modelling basic optical and biophysical
constraints, and by making measurements. The appropriate measure of benefit is
the quantity of information coded, in bits. The cost is the consumption of A TP.
Cost-benefit relationships follow the law of diminishing returns and this increases
the pressure to reduce sense organs to the essential minimum. Ultimately the
costs and the uses made of information by individuals should be related to fitness.
Key words Vision, allometry, information theory, cost-benefit, energy
1 Introduction
Sensory ecology is the study of the contributions made by sense organs to
ecology and behavior (Lythgoe 1979). These contributions are of crucial
importance because sensory information enables animals to make the adaptive
physiological and behavioral responses that permit survival and reproduction. It
follows that much of sensory ecology concerns adaptations of sense organs and
sensory processes that, by extracting and processing the appropriate sensory
information, enable a particular species to pursue a particular life-style in a
particular habitat. The extent and variety of these adaptations, together with the
subtle differences observed between closely related species, suggest that sensory
function has a large effect on fitness. Significant costs are being balanced by
Simon B. Laughlin
Department of Zoology, University of Cambridge, Downing St, Cambridge CB2
3EJ, UK
Abstract
To better understand the adaptations of form to function that constitute much of
contemporary visual ecology, we examine the costs and the benefits associated
with the first stages of vision. Taking the blowfly as a model, the major metabolic
costs are the metabolic energy used to support the mass of the eye during
locomotion and the metabolic energy used to generate electrical signals. These
account for 10% of total metabolic rate at rest, and 3% in flight. This significant
contribution to total metabolic rate helps to explain the numerous adaptations that
maximize the efficiency with which the components of sensory systems capture
and encode information. To further understand these adaptations, metabolic costs
are related to sensory benefit by modelling basic optical and biophysical
constraints, and by making measurements. The appropriate measure of benefit is
the quantity of information coded, in bits. The cost is the consumption of A TP.
Cost-benefit relationships follow the law of diminishing returns and this increases
the pressure to reduce sense organs to the essential minimum. Ultimately the
costs and the uses made of information by individuals should be related to fitness.
Key words Vision, allometry, information theory, cost-benefit, energy
1 Introduction
Sensory ecology is the study of the contributions made by sense organs to
ecology and behavior (Lythgoe 1979). These contributions are of crucial
importance because sensory information enables animals to make the adaptive
physiological and behavioral responses that permit survival and reproduction. It
follows that much of sensory ecology concerns adaptations of sense organs and
sensory processes that, by extracting and processing the appropriate sensory
information, enable a particular species to pursue a particular life-style in a
particular habitat. The extent and variety of these adaptations, together with the
subtle differences observed between closely related species, suggest that sensory
function has a large effect on fitness. Significant costs are being balanced by