From PhilPapers forum Philosophy of Mind:

2010-11-08
The time-lag argument for the representational theory of perception
Reply to Derrick Farnell
Derrick Farnell
Here is version #387:

  1. The process of visual perception takes 100 ms when viewing your immediate surroundings.

  2. Therefore, given that the field of vision is the input to the visual process, and your visual field is the output, visible events in the field of vision won't occur in your visual field for 100 ms when viewing your immediate surroundings.

  3. The light pulse from a camera flash has a typical duration of 1 ms, and the brief additional illumination of your immediate surroundings by a camera flash is a clearly visible event.

  4. Therefore, if, when viewing your immediate surroundings, the field of vision receives additional illumination from a camera flash between the points in time T and T + 1 ms, then this event won't occur in your visual field for 100 ms, occurring between T + 100 ms and T + 101 ms - as this diagram shows:

  5. However, a specific event occurs solely between two specific points in time, and so can't itself also occur between two later points in time.

  6. Therefore, if the event in reality occurs between T and T + 1 ms, then what occurs between T + 100 ms and T + 101 ms in your visual field can't literally be the event itself.

  7. Therefore, what you actually experience visually between T + 100 ms and T + 101 ms must be merely a subsequent mental representation of the field of vision receiving the additional illumination between T and T + 1 ms.

  8. There's no reason why the fundamental nature of your visual experience of the scene in front of your eyes should change depending on the level of illumination of that scene.

  9. Therefore, your visual field must always be merely a mental representation of the field of vision at the start of the visual process.


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