# Several basic questions regarding contrast threshold

**URL:** <https://psychtoolbox.discourse.group/t/several-basic-questions-regarding-contrast-threshold/1226>\
**Category:** Uncategorized\
**Created:** [July 29, 2002, 10:13pm UTC](https://psychtoolbox.discourse.group/t/several-basic-questions-regarding-contrast-threshold/1226 "2002-07-29T22:13:22Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Allen\_Ingling](https://avatars.discourse-cdn.com/v4/letter/a/a183cd/32.png) [@Allen\_Ingling](https://psychtoolbox.discourse.group/u/Allen_Ingling)\
**Post date:** [July 29, 2002, 10:13pm UTC](https://psychtoolbox.discourse.group/t/several-basic-questions-regarding-contrast-threshold/1226/1 "2002-07-29T22:13:22Z")

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Hi,  
I want to run a contrast sensitivity test for different spatial freqwuency   
and I was told that the contrast threshold demo of psychtoll is good   
enough for this. I have several question regarding to this:  
  
1- does one needs to calibrate the values for contrast by measuring the   
actual intensities of the screen before running the test? (or maybe the   
program can adjust to this autimatically ??)  
  
2- Can one run the test on laptop ((using lcd screen)? is it reliable?  
  
3- What is the recomended resolution for being able to have good stimuli   
for high SF (such as 30 c/d)  
  
4- in the demo the program run for 20 trials only - is it reasonable to   
assum convergence of the algorithm so early? or it inly for demo purposes?  
  
5- when is running without noise and withou gaussian envelope - the signal   
is always detectable. Is there a way to control this?  
  
Thank you  
Orna Rosenthal