Browsing by Subject "colour vision"

Sort by: Order: Results:

Now showing items 1-4 of 4
  • Witzel, Christoph; Olkkonen, Maria; Gegenfurtner, Karl R. (2018)
    According to the memory colour effect, the colour of a colour-diagnostic object is not perceived independently of the object itself. Instead, it has been shown through an achromatic adjustment method that colour-diagnostic objects still appear slightly in their typical colour, even when they are colourimetrically grey. Bayesian models provide a promising approach to capture the effect of prior knowledge on colour perception and to link these effects to more general effects of cue integration. Here, we model memory colour effects using prior knowledge about typical colours as priors for the grey adjustments in a Bayesian model. This simple model does not involve any fitting of free parameters. The Bayesian model roughly captured the magnitude of the measured memory colour effect for photographs of objects. To some extent, the model predicted observed differences in memory colour effects across objects. The model could not account for the differences in memory colour effects across different levels of realism in the object images. The Bayesian model provides a particularly simple account of memory colour effects, capturing some of the multiple sources of variation of these effects.
  • Villani, Giovanna Marques (Helsingin yliopisto, 2020)
    Hypotheses to explain the emergence and maintenance of trichromacy in primates have long focused on the role of diet, often suggesting trichromats are better able to detect ripe fruits and nutritious leaves. However, many neotropical primate species also need to avoid eating conspicuous food items like insects that have evolved to warn potential predators of their unprofitability. This factor has largely been ignored in work on primate colour vision. We suggest here that dichromatic and trichromatic individuals vary in their ability to learn about conspicuous but unprofitable food and that trichromats could be more effective than dichromats at detecting conspicuous unprofitable prey. To test this hypothesis, three females and one male white-faced saki (Pithecia pithecia) participated in behavioral experiments at Korkeasaari zoo (Helsinki, Finland) where choice boxes were presented marked with two symbols against a green background. Only trichromats could discriminate orange symbols that provided an unprofitable food reward from the more profitable green symbols. Each saki made 80 choices over 10 trials. While we did not detect any evidence for learning about symbol profitability, we found two females significantly avoided the conspicuous prey meaning they received greater food rewards than the dichromat male and one putative dichromat female. Further analysis is needed of the opsin genes of the females in this study to confirm the role of unprofitable food in Saki colour vision.
  • Yovanovich, Carola A. M.; Koskela, Sanna M.; Nevala, Noora; Kondrashev, Sergei L.; Kelber, Almut; Donner, Kristian (2017)
    The presence of two spectrally different kinds of rod photoreceptors in amphibians has been hypothesized to enable purely rod-based colour vision at very low light levels. The hypothesis has never been properly tested, so we performed three behavioural experiments at different light intensities with toads (Bufo) and frogs (Rana) to determine the thresholds for colour discrimination. The thresholds of toads were different in mate choice and prey-catching tasks, suggesting that the differential sensitivities of different spectral cone types as well as task-specific factors set limits for the use of colour in these behavioural contexts. In neither task was there any indication of rod-based colour discrimination. By contrast, frogs performing phototactic jumping were able to distinguish blue from green light down to the absolute visual threshold, where vision relies only on rod signals. The remarkable sensitivity of this mechanism comparing signals from the two spectrally different rod types approaches theoretical limits set by photon fluctuations and intrinsic noise. Together, the results indicate that different pathways are involved in processing colour cues depending on the ecological relevance of this information for each task. This article is part of the themed issue 'Vision in dim light'.
  • Yovanovich, Carola A. M.; Koskela, Sanna M.; Nevala, Noora; Kondrashev, Sergei L.; Kelber, Almut; Donner, Kristian (The Royal Society of Chemistry, 2017)
    The presence of two spectrally different kinds of rod photoreceptors in amphibians has been hypothesized to enable purely rod-based colour vision at very low light levels. The hypothesis has never been properly tested, so we performed three behavioural experiments at different light intensities with toads (Bufo) and frogs (Rana) to determine the thresholds for colour discrimination. The thresholds of toads were different in mate choice and prey-catching tasks, suggesting that the differential sensitivities of different spectral cone types as well as task-specific factors set limits for the use of colour in these behavioural contexts. In neither task was there any indication of rod-based colour discrimination. By contrast, frogs performing phototactic jumping were able to distinguish blue from green light down to the absolute visual threshold, where vision relies only on rod signals. The remarkable sensitivity of this mechanism comparing signals from the two spectrally different rod types approaches theoretical limits set by photon fluctuations and intrinsic noise. Together, the results indicate that different pathways are involved in processing colour cues depending on the ecological relevance of this information for each task. This article is part of the themed issue 'Vision in dim light'.