A note on the horopter

By assuming the fixity (but not the symmetry) of corresponding points on the two retinae, it is possible to derive the equation of any horopter when one is known. In particular when, as experiment shows, one horopter is linear, then all horopters must be conics. These have the form given by Ogle, but whereas Ogle leaves one parameter undetermined at each fixation, on our assumption the only arbitrary parameter is determined by the position of the linear horopter.     

A note on the reafference principle

Two alternative circuits to realize the reafference principle are considered and quantitatively analyzed. Both are combinations of a conventional control loop with negative feedback and linear transfer functions, as well as of an efference copy branch. The feedback control loop compensates for passive movements of the body or of its parts, and generates active movements, whenever the set point differs from zero. The efference copy branch should eliminate sensory messages to higher brain centres during active body movements and, thus, mediate perceptual stability. In one of the combinations, discussed also briefly by Mittelstaedt (1971), the efference copy branch interacts with and thus modifies the properties of the feedback loop. The performance of this circuit is very sensitive to variations of the system parameters and, therefore, requires precise adjustment. When the transfer function of the efference copy branch exactly matches that of the feedback loop and its gain amounts to 1, this circuit performs as a control loop with an integrator in the negative feedback branch: there is no steady state control error. However, for certain parameter combination the circuit becomes unstable. In the alternative circuit proposed here, the efference copy branch does not interfere with the feedback loop. It is robust against parameter variations. The transient properties of both circuits are described under simplified assumptions regarding the linear transfer functions in the different branches.     

A note on the measurement of redundancy

Plant Ecology - The present paper points out a simpler method for computing the redundancy coefficient proposed by Orlóci (1975) using the inverse of the variance-covariance matrix. It is...     

A note on the cybernetics of segregation

The results of a preceding paper (Progress in Biocybernetics,2, Elsevier, 1965) are generalized to express the intensity of anti-Negro feelings, and of the segregation index as functions of the percentage of Negroes in the population. Previous results are applied to effects of migration of Negroes from regions of strong racial prejudice to regions of lesser racial prejudice.     

A note on the cybernetics of segregation

The results of a preceding paper (Progress in Biocybernetics,2, Elsevier, 1965) are generalized to express the intensity of anti-Negro feelings, and of the segregation index as functions of the percentage of Negroes in the population. Previous results are applied to effects of migration of Negroes from regions of strong racial prejudice to regions of lesser racial prejudice.     

A note on the geometrization of biology

In connection with a recently proposed topological model of an organism (Bull. Math. Biophysics,18, 31–56, 1956), it is pointed out that the dependence of some properties of the studied topological spaces on the type of space in which they are imbedded reflects some aspects of the dependence of the organism on its environment.     

A note on the shape of the erythrocyte

Variational calculus is used to derive an equation for the shape of the cross section of a human red blood cell, the objective being the maximization of the surface area/volume ratio. Comparison to previous work is presented.     

A note on the diffusion drag forces

A formal derivation of the expression for the diffusion drag force is given. The expression involves the coefficient of diffusion of the solute through the solvent and the coefficient of diffusion which the solute would posses if it diffused through itself in the form of a gas, in the absence of the solvent.