Contrast Thresholds of the Human Eye

Blackwell, H. Richard

doi:10.1364/josa.36.000624

Cited by 793 publications

(395 citation statements)

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“…It seems probable that Secchi disk diamcter, at least in the range used, does not affect Zsn because the ZflD depths are not sufficiently great to cause the angular subtense of the disk to affect the visibility of the disk ( see Blackwell 1946).…”

Section: And Discussionmentioning

confidence: 99%

The Secchi Disk in Turbid Coastal Waters1

Holmes

1970

Limnology & Oceanography

254

148

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Section: And Discussionmentioning

confidence: 99%

The Secchi Disk in Turbid Coastal Waters1

Holmes

1970

Limnology & Oceanography

254

148

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“…If an object's apparent contrast at a given range is smaller than the observer's contrast threshold, the object is said to invisible. Human contrast threshold values as a function of apparent luminance and object angular size were taken from prior work (81). These values were transformed into functions of apparent luminance, angular resolution, and angular size of the object, where angular resolution was chosen to be the diffraction limit, allowing for an implicit pupil diameter and visual range relationship.…”

Section: Methodsmentioning

confidence: 99%

“…Finally, we tested alternative values for key vision model parameters (SI Appendix, Table S2). The new contrast threshold values (Kt) were calculated from relating the human contrast threshold curve (81) to the goldfish contrast threshold (88). The functions relating angular size, contrast threshold, and luminance [Kt = Ψ(D, T, r, L)] (definitions are in SI Appendix, Table S1) for both goldfish and human were similar enough to be approximated with a shift equal to the mean percentage difference between the two datasets.…”

Section: Methodsmentioning

confidence: 99%

Massive increase in visual range preceded the origin of terrestrial vertebrates

MacIver

Schmitz

Mugan

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The evolution of terrestrial vertebrates, starting around 385 million years ago, is an iconic moment in evolution that brings to mind images of fish transforming into four-legged animals. Here, we show that this radical change in body shape was preceded by an equally dramatic change in sensory abilities akin to transitioning from seeing over short distances in a dense fog to seeing over long distances on a clear day. Measurements of eye sockets and simulations of their evolution show that eyes nearly tripled in size just before vertebrates began living on land. Computational simulations of these animal's visual ecology show that for viewing objects through water, the increase in eye size provided a negligible increase in performance. However, when viewing objects through air, the increase in eye size provided a large increase in performance. The jump in eye size was, therefore, unlikely to have arisen for seeing through water and instead points to an unexpected hybrid of seeing through air while still primarily inhabiting water. Our results and several anatomical innovations arising at the same time suggest lifestyle similarity to crocodiles. The consequent combination of the increase in eye size and vision through air would have conferred a 1 million-fold increase in the amount of space within which objects could be seen. The "buena vista" hypothesis that our data suggest is that seeing opportunities from afar played a role in the subsequent evolution of fully terrestrial limbs as well as the emergence of elaborated action sequences through planning circuits in the nervous system. fish-tetrapod transition | vision | visual ecology | terrestriality | prospective cognition B efore terrestrial vertebrates arose, their ancestors inhabited underwater environments, where vision is highly compromised compared with vision above water. The visual difference between life in water and life above it is comparable with driving fast on a foggy road, where our responses must be rapid and simple, vs. driving in clear daylight conditions, where deliberation over more complex choices is enabled by the vast increase in sensory range. Nonetheless, although an immense quantity of work has been done on the emergence of limbs during the evolution of land vertebrates, how visual capability changed during the transition from water to land has not been explored. In part, this lack of exploration is because computational visual ecology-necessary to interpret the fossil data-has not been combined with early tetrapod paleontology. Through combining these disciplines, here we probe the evolutionary history of the switch in our visual sensory ecology from water to air. Surprisingly, our results show that eyes tripled in size just before full-time life on land evolved. Convergent lines of evidence, including our own, strongly support the hypothesis that a crocodilian ecotype-using the greatly enhanced visual capabilities conferred by vision through air to prey on the bounty of unexploited invertebrates that long preceded the vertebrates onto ...

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“…A more realistic liminal contrast value of 0.05 is used instead of Koschmieder's value of 0.02, as suggested by Blackwell (1946). The visibility parameterization used in the DM follows Clark et al (2008).…”

Section: Visibility Parameterizationmentioning

confidence: 99%

An operational fog prediction system for Delhi using the 330 m Unified Model

Jayakumar

Rajagopal

Boutle

et al. 2017

Atmospheric Science Letters

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Funding information NASA/HQWe introduce the National Centre for Medium Range Weather Forecasting's (NCMRWF) high-resolution (330 m) Unified Model implementation targeted at fog and visibility prediction over Delhi, the "Delhi Model" (DM). The requirement for running the DM in real time is that Delhi is highly vulnerable to fogrelated issues and that low visibility conditions affect both airborne and ground transport during winter months. Enhanced orographic features at 330 m resolution, in conjunction with other surface boundary conditions used by the DM, have led to improvements in the simulation of spatio-temporal variability of visibility. During the winter season, the increased levels of pollution can have a significant impact on fog, or smog formation. Sensitivity experiments carried out using specified aerosol mass concentrations show that the visibility predicted by the DM is highly sensitive to the presence of aerosol. The impact of the urban heat island on visibility prediction is also investigated using recent high-resolution land use data from the Indian Space Research Organisation (ISRO) in the model.

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Contrast Thresholds of the Human Eye

Cited by 793 publications

References 0 publications

The Secchi Disk in Turbid Coastal Waters1

The Secchi Disk in Turbid Coastal Waters1

Massive increase in visual range preceded the origin of terrestrial vertebrates

An operational fog prediction system for Delhi using the 330 m Unified Model

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