QUEST Grain Size

1
Hi all,

I am trying to use QUEST to determine the 75% threshold of distinguishing a stimulus in the periphery of the visual field.

To this end, I am letting QUEST vary the size of the stimuli. I am using a linear scale (if anyone happens to have a better suggestion that would be useful; I did this for lack of a better scale). However, I need the stepsize to vary in integers, as there are no half-pixels or 0.2715 pixels.

If I set the "grain" variable to be 1, however, I still receive non-integer values when I ask for a new value to use for the next trial with QuestQuantile.

2 Questions:

Am I misunderstanding the purpose of the "grain" variable here?

Would my best bet be to just round the value given out by QuestQuantile?

Thanks a lot in advance,
Jan
2
Yes, just round the output and then update quest with the actual value tested - the quest demo shows how this is done.

On Wed, Dec 12, 2012 at 7:59 AM, jan.freyberg <jan.freyberg@...> wrote:

Hi all,

I am trying to use QUEST to determine the 75% threshold of distinguishing a stimulus in the periphery of the visual field.

To this end, I am letting QUEST vary the size of the stimuli. I am using a linear scale (if anyone happens to have a better suggestion that would be useful; I did this for lack of a better scale). However, I need the stepsize to vary in integers, as there are no half-pixels or 0.2715 pixels.

If I set the "grain" variable to be 1, however, I still receive non-integer values when I ask for a new value to use for the next trial with QuestQuantile.

2 Questions:

Am I misunderstanding the purpose of the "grain" variable here?

Would my best bet be to just round the value given out by QuestQuantile?

Thanks a lot in advance,
Jan