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Darren Koenig, Heidi Hofer; The absolute threshold of cone vision is relatively insensitive to the criteria for seeing. Journal of Vision 2007;7(15):74. doi: 10.1167/7.15.74.
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© ARVO (1962-2015); The Authors (2016-present)
In rod-mediated vision the absolute threshold for seeing is heavily dependent on the subjective response criterion. Sakitt (1972) demonstrated that rod thresholds can be reduced by more than ∼0.4 log units by consciously adopting more lenient criteria than usually employed in a ‘yes-no’ detection experiment. These experiments implied access to information from every quantum absorption in the rod system. It is unknown whether cone-mediated vision also has these properties. We repeated Sakitt's experiment for a cone-dominated, threshold level detection task. A 550 nm, 30 ms point source with a full-width at half maximum of ∼1 arcmin on the retina was foveally presented at three intensity levels with an equivalent number of blank trials. Subjects recorded whether or not the spot was seen using 6 ratings, ranging from definitely not seen to definitely seen, respectively. In contrast to rod thresholds, we found that cone thresholds could not be reduced more than ∼0.15 log units by intentionally adopting more lenient detection criteria. Unlike the rod system, our data is consistent with the existence of an internal, fixed, threshold below which sensory information cannot be accessed in the determination of whether or not a stimulus is seen. Sakitt B. 1972. Counting every quantum. J. Physiol. 223: 131–50.
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