Do you see the point? : Visual thresholds for single targets in budgerigars
(2024)- Abstract
- The vision of birds has been extensively studied, and alot is known about what they are able to see contrast sensitivity and acuity, in different light intensities, is known Still, visual perception depends on a combination of many stimulus parameters, which can make it difficult to predict the visibility of ecologically relevant stimuli.
In this doctoral thesis I have investigate visual thresholds of budgerigars (Melopittacus undulatus) using stimuli designed to better match visual tasks which birds encounter naturally. Starting from questions regarding the visual thresholds of birds in ecologically relevant tasks, I have used a psychophysical approach in an attempt to reveal their limits of vision.
A number of different species,... (More) - The vision of birds has been extensively studied, and alot is known about what they are able to see contrast sensitivity and acuity, in different light intensities, is known Still, visual perception depends on a combination of many stimulus parameters, which can make it difficult to predict the visibility of ecologically relevant stimuli.
In this doctoral thesis I have investigate visual thresholds of budgerigars (Melopittacus undulatus) using stimuli designed to better match visual tasks which birds encounter naturally. Starting from questions regarding the visual thresholds of birds in ecologically relevant tasks, I have used a psychophysical approach in an attempt to reveal their limits of vision.
A number of different species, including umans, are able to detect visual targets below the resolving limit of the retinal mosaik, given they provide enough contrast to the background. In Paper I we tested the detection threshold for circular single dark targets against a brighter background, the single target acuity, of budgerigars. We found that, in contrast to humans, the single target acuity of budgerigars is not higher than their grating acuity. Detection threshold varied with luminance contrast, in a similar way as for gratings, but also with the target luminance profile (0.065° for sinusoidal wave and 0.098° for square-wave shaped target). We concluded that the low contrast sensitivity of budgerigars likely limits their single target acuity.
The single target acuity of budgerigars was further investigated in Paper II were we added a semi-random movement (1.69 degrees s−1) to a “square-wave” single target. Motion can increase the saliency of visual targets through attentional capture, but has also been shown to increase the luminance contrast sensitivity of budgerigars for gratings. Despite this, the single target acuity for moving targets (0.107°) did not differ from the single target acuity for static targets measured in Paper I.
In Paper III we explored the luminance vision of budgerigars immediately after experiencing a decrease in light intensity. Our goal was to simulate the light intensity dynamics experienced by cavity-nesting birds upon nest-entry. We tested the luminance detection, and discrimination, threshold for circular grey targets (9.6 degrees) on a black background as the birds went from a bright environment into a darker facility. The experiments included thresholds measured at illumination drops of ranging between 0.5 and 3.5 log units. Despite having no time limits, the birds made a response within about 1 second after stimulus onset (which was at the same time as the light decrease), and did not wait to adapt to the lower light intensities. The luminance detection threshold was in the same range when the decrease in illumination was 1.7-3.5 log units, while it was considerably higher when the illumination only dropped by 0.5 log units. The birds were able to discriminate between two grey targets with Weber fractions between 0.41 and 0.54 for all light levels. Although the visual performance is inferior to previously measured contrast- or brightness discrimination in fully adapted budgerigars, it is consistent with Weber’ law. Thus, our result indicates that budgerigars partially adapt to light drops of at least -3.5 log units within ~1 second.
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Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/98eb0195-043e-49be-b06a-bc93628a4786
- author
- Chaib, Sandra LU
- supervisor
-
- Almut Kelber LU
- Olle Lind LU
- Eric Warrant LU
- Jan-Åke Nilsson LU
- opponent
-
- Professor Roberts, Nicholas, School of Biological Sciences, University of Bristol
- organization
- publishing date
- 2024
- type
- Thesis
- publication status
- published
- subject
- keywords
- Bird vision, Spatial vision, Budgerigar, animal psychophysics, Bird vision, Spatial vision, Budgerigar, Animal psychophysics
- pages
- 140 pages
- publisher
- Lund University
- defense location
- Blå Hallen, Biologihuset, Sölvegatan 35
- defense date
- 2024-10-03 09:00:00
- ISBN
- 978-91-8104-161-3
- 978-91-8104-161-0
- language
- English
- LU publication?
- yes
- id
- 98eb0195-043e-49be-b06a-bc93628a4786
- date added to LUP
- 2024-09-06 12:37:40
- date last changed
- 2025-04-04 14:38:46
@phdthesis{98eb0195-043e-49be-b06a-bc93628a4786,
abstract = {{The vision of birds has been extensively studied, and alot is known about what they are able to see contrast sensitivity and acuity, in different light intensities, is known Still, visual perception depends on a combination of many stimulus parameters, which can make it difficult to predict the visibility of ecologically relevant stimuli.<br/>In this doctoral thesis I have investigate visual thresholds of budgerigars (Melopittacus undulatus) using stimuli designed to better match visual tasks which birds encounter naturally. Starting from questions regarding the visual thresholds of birds in ecologically relevant tasks, I have used a psychophysical approach in an attempt to reveal their limits of vision.<br/>A number of different species, including umans, are able to detect visual targets below the resolving limit of the retinal mosaik, given they provide enough contrast to the background. In Paper I we tested the detection threshold for circular single dark targets against a brighter background, the single target acuity, of budgerigars. We found that, in contrast to humans, the single target acuity of budgerigars is not higher than their grating acuity. Detection threshold varied with luminance contrast, in a similar way as for gratings, but also with the target luminance profile (0.065° for sinusoidal wave and 0.098° for square-wave shaped target). We concluded that the low contrast sensitivity of budgerigars likely limits their single target acuity.<br/>The single target acuity of budgerigars was further investigated in Paper II were we added a semi-random movement (1.69 degrees s−1) to a “square-wave” single target. Motion can increase the saliency of visual targets through attentional capture, but has also been shown to increase the luminance contrast sensitivity of budgerigars for gratings. Despite this, the single target acuity for moving targets (0.107°) did not differ from the single target acuity for static targets measured in Paper I.<br/>In Paper III we explored the luminance vision of budgerigars immediately after experiencing a decrease in light intensity. Our goal was to simulate the light intensity dynamics experienced by cavity-nesting birds upon nest-entry. We tested the luminance detection, and discrimination, threshold for circular grey targets (9.6 degrees) on a black background as the birds went from a bright environment into a darker facility. The experiments included thresholds measured at illumination drops of ranging between 0.5 and 3.5 log units. Despite having no time limits, the birds made a response within about 1 second after stimulus onset (which was at the same time as the light decrease), and did not wait to adapt to the lower light intensities. The luminance detection threshold was in the same range when the decrease in illumination was 1.7-3.5 log units, while it was considerably higher when the illumination only dropped by 0.5 log units. The birds were able to discriminate between two grey targets with Weber fractions between 0.41 and 0.54 for all light levels. Although the visual performance is inferior to previously measured contrast- or brightness discrimination in fully adapted budgerigars, it is consistent with Weber’ law. Thus, our result indicates that budgerigars partially adapt to light drops of at least -3.5 log units within ~1 second.<br/>}},
author = {{Chaib, Sandra}},
isbn = {{978-91-8104-161-3}},
keywords = {{Bird vision; Spatial vision; Budgerigar; animal psychophysics; Bird vision; Spatial vision; Budgerigar; Animal psychophysics}},
language = {{eng}},
publisher = {{Lund University}},
school = {{Lund University}},
title = {{Do you see the point? : Visual thresholds for single targets in budgerigars}},
url = {{https://lup.lub.lu.se/search/files/194638228/Avhandling_Sandra_Chaib_LUCRIS.pdf}},
year = {{2024}},
}