J Daugman | PubMed Health

PubMed2001

Epigenetic randomness, complexity and singularity of human iris patterns.

We investigated the randomness and uniqueness of human iris patterns by mathematically comparing 2.3 million different pairs of eye images. The phase structure of each iris pattern was extracted by demodulation with quadrature wavelets spanning several scales of analysis. The resulting distribution of phase sequence variation among different eyes was precisely binomial, revealing 244 independent degrees of freedom. This amount of statistical variability corresponds to an entropy (information density) of about 3.2 bits mm(-2) over the iris. It implies that the probability of two different irides agreeing by chance in more than 70% of their phase sequence is about one in 7 billion. We also compared images of genetically identical irides, from the left and right eyes of 324 persons, and from monozygotic twins. Their relative phase sequence variation generated the same statistical distribution as did unrelated eyes. This indicates that apart from overall form and colour, iris patterns are determined epigenetically by random events in the morphogenesis of this tissue. The resulting diversity, and the combinatorial complexity created by so many dimensions of random variation, mean that the failure of a simple test of statistical independence performed on iris patterns can serve as a reliable rapid basis for automatic personal identification.

Functional Laterality↗

PubMed1984

Use of Gabor elementary functions to probe receptive field substructure of posterior inferotemporal neurons in the owl monkey.

The large receptive fields of inferotemporal neurons in the owl monkey were studied with visual stimuli whose luminance profiles were one-dimensional Gabor functions, i.e. sinusoidal gratings within Gaussian envelopes. The members of one set of such patterns all had a full bandwidth at half-amplitude of 0.8 octaves, but different center frequencies and spatial extents. These spatially restricted stimuli were ideal for determining whether one or more than one spatial frequency band projected onto discrete subsections of the neuron's receptive field. The other set of Gabor stimuli comprised sine waves within Gaussian envelopes of constant size, but with different center frequencies and hence different bandwidths. These stimuli allowed assessment of the neuron's spatial frequency selectivity across the full breadth of its receptive field. Results suggest that only one orientation band and one spatial frequency band provide an input onto each inferotemporal neuron under our experimental conditions. The preferred spatial frequencies found (0.2-0.6 c/deg) were all in the very low spatial frequency range for this animal. Calculations show that about 3.5-7.0 full cycles of the optimal grating usually cover the full width of the receptive field, but the observed spatial frequency tuning is not nearly as sharp as that which would be predicted according to phase coherent linear summation. Moreover, at the preferred spatial frequency, the peak response to gratings in the constant aperture series was generally less than the response to the same preferred spatial frequency in the constant relative bandwidth series. These results suggest either incomplete phase coherent summation from contributing subgroups, non-linear processing, or both.

Animals↗