Thomas W. Cronin

Bioinspired polarization imaging sensors: from circuits and optics to signal processing algorithms and biomedical applications

In this paper, we present recent work on bioinspired polarization imaging sensors and their applications in biomedicine. In particular, we focus on three different aspects of these sensors. First, we describe the electro-optical challenges in realizing a bioinspired polarization imager, and in particular, we provide a detailed description of a recent low-power complementary metal-oxide-semiconductor (CMOS) polarization imager. Second, we focus on signal processing algorithms tailored for this new class of bioinspired polarization imaging sensors, such as calibration and interpolation. Third, the emergence of these sensors has enabled rapid progress in characterizing polarization signals and environmental parameters in nature, as well as several biomedical areas, such as label-free optical neural recording, dynamic tissue strength analysis, and early diagnosis of flat cancerous lesions in a murine colorectal tumor model. We highlight results obtained from these three areas and discuss future applications for these sensors.

Polarization vision seldom increases the sighting distance of silvery fish

Although the function of polarization vision, the ability to discern the polarization characteristics of light, is well established in many terrestrial and benthic species, its purpose in pelagic species (squid and certain fish and crustaceans) is poorly understood [1]. A long-held hypothesis is that polarization vision in open water is used to break the mirror camouflage of silvery fish, as biological mirrors can change the polarization of reflected light [2,3]. Although, the addition of polarization information may increase the conspicuousness of silvery fish at close range, direct evidence that silvery fish - or indeed any pelagic animal - are visible at longer distances using polarization vision rather than using radiance (i.e. brightness) vision is lacking. Here we show, using in situ polarization imagery and a new visual detection model, that polarization vision does not in fact appear to allow viewers to see silvery fish at greater distances.

Comment on "Open-ocean fish reveal an omnidirectional solution to camouflage in polarized environments"

Brady et al. (Reports, 20 November 2015, p. 965) claimed that the silvery sides of certain fish are cryptic when viewed by animals with polarization sensitivity, which they termed “polarocrypsis.” After examining their evidence, we find this claim to be unsupported due to (i) pseudoreplication, (ii) confounding polarization contrast with intensity contrast, and (iii) measurements taken at very shallow depths.

Bioinspired Polarization Imaging Sensors: From Circuits and Optics to Signal Processing Algorithms and Biomedical Applications: Analysis at the focal plane emulates nature's method in sensors to image and diagnose with polarized light.

In this paper, we present recent work on bioinspired polarization imaging sensors and their applications in biomedicine. In particular, we focus on three different aspects of these sensors. First, we describe the electro-optical challenges in realizing a bioinspired polarization imager, and in particular, we provide a detailed description of a recent low-power complementary metal-oxide-semiconductor (CMOS) polarization imager. Second, we focus on signal processing algorithms tailored for this new class of bioinspired polarization imaging sensors, such as calibration and interpolation. Third, the emergence of these sensors has enabled rapid progress in characterizing polarization signals and environmental parameters in nature, as well as several biomedical areas, such as label-free optical neural recording, dynamic tissue strength analysis, and early diagnosis of flat cancerous lesions in a murine colorectal tumor model. We highlight results obtained from these three areas and discuss future applications for these sensors.

A different view: sensory drive in the polarized-light realm

Abstract Sensory drive, the concept that sensory systems primarily evolve under the influence of environmental features and that animal signals are evolutionarily shaped and tuned by these previously existing sensory systems, has been thoroughly studied regarding visual signals across many animals. Much of this work has focused on spectral aspects of vision and signals. Here, I review work on polarized-light signals of animals and relate these to what is known of polarization visual systems, polarized-light aspects of visual scenes, and polarization-related behavior (e.g., orientation, habitat-finding, contrast enhancement). Other than the broad patterns of scattered polarized light in the sky, most polarization in both terrestrial and aquatic environments results from either reflection or scattering in the horizontal plane. With overhead illumination, horizontal features such as the surfaces of many leaves or of air: water interfaces reflect horizontal polarization, and water scatters horizontally polarized light under most conditions. Several animal species have been demonstrated to use horizontally polarized light fields or features in critical aspects of their biology. Significantly, most biological signals are also horizontally polarized. Here, I present relevant polarization-related behavior and discuss the hypothesis that sensory drive has evolutionarily influenced the structure of polarization signals. The paper also considers the evolutionary origin of circular polarization vision and circularly polarized signals. It appears that this class of signals did not evolve under the influence of sensory drive. The study of signals based on polarized light is becoming a mature field of research.