09-04-2020, 03:54 PM
Visual angle is the angle that an object or stimulus creates on the retina of the eye. Imagine two lines extending from the center of your eye to the outer edges of an object you are looking at; the angle between those two lines is the visual angle. In the diagram below visual angle (V) is defined as the angle formed by rays extending from the eye (O) to points A and B, which could represent the two edges of an object, or two points on a visual display.
(diagram by author Ojosepa; used under Creative Commons license https://en.wikipedia.org/wiki/File:EyeOpticsV400y.jpg)
In vision science, reporting measurements in degrees of visual angle (°), rather than in physical units like centimeters or pixels, is standard practice. This is because visual angle provides a universal measure that is independent of viewing distance.
For example, a 5 cm stimulus is meaningless without knowing how far away it was from the participant. However, a 5° stimulus is a precise measurement that allows for easy and accurate replication in other labs, regardless of their specific monitor size or setup.
The EyeLink system uses degrees of visual angle as its fundamental unit for calculating saccade velocities and measuring saccade amplitudes, ensuring that these metrics are standardized and comparable across different studies and experimental setups.
In order for these calculations to be accurate, it is important that your Host PC has been configured correctly, and knows the dimensions and distance of your monitor. Please see the following post for more details: Our website features a more detailed discussion of visual angle, along with a helpful online calculator for converting between pixels and degrees.
(diagram by author Ojosepa; used under Creative Commons license https://en.wikipedia.org/wiki/File:EyeOpticsV400y.jpg)
In vision science, reporting measurements in degrees of visual angle (°), rather than in physical units like centimeters or pixels, is standard practice. This is because visual angle provides a universal measure that is independent of viewing distance.
For example, a 5 cm stimulus is meaningless without knowing how far away it was from the participant. However, a 5° stimulus is a precise measurement that allows for easy and accurate replication in other labs, regardless of their specific monitor size or setup.
The EyeLink system uses degrees of visual angle as its fundamental unit for calculating saccade velocities and measuring saccade amplitudes, ensuring that these metrics are standardized and comparable across different studies and experimental setups.
In order for these calculations to be accurate, it is important that your Host PC has been configured correctly, and knows the dimensions and distance of your monitor. Please see the following post for more details: Our website features a more detailed discussion of visual angle, along with a helpful online calculator for converting between pixels and degrees.