Black Box IEEE 1284 Podręcznik Użytkownika Pobierz pdf (Strona 62)

Page 62 of 98 The Black Box Toolkit

events that have been detected. Lines 5 through 8 show events that were generated by

the BBTK and fed into the remote PC to simulate a human making a response.

8.5.1.1. Analysing visual stimulus event data obtained from monitoring a TFT

At this point we have two options. One is to make use of the spreadsheet for analysis and

the other to make use of the two measurement cursors. Because we are using a TFT as a

display device this offers discrete on and off timing measures together with a constant on

period (with no refresh). As a result we can simply examine the timings for the relevant line

in the lower spreadsheet view. When we examine line 3 we can see that display times for

each image presentation varied between 363ms and 375ms. Obviously this is significantly

longer than the expected display time of 300ms.

8.5.1.2. Analysing visual stimulus event data obtained from monitoring a CRT

However, if we were using a standard CRT the duration column would show the duration

of each refresh rather than the total image duration. In the standard CRT example shown

below we can see each refresh occurring at 10ms intervals (1,255-1245=10ms) indicating

the monitor was being driven at 100Hz. The duration gives an indication on the phosphor

decay time which in this case is around 3ms. You should be aware that the duration time

can be effected by the brightness of the screen and the luminance sensitivity threshold

settings of the BBTK.

Typically we would use the measurement cursors in order to find out exactly how long the

image stimulus had been displayed. You also have the option to analyse the spreadsheet

data further should you wish.

By right clicking anywhere on the plot a pop-up menu will appear. If you click on “Measure”

two cursors will be activated. These can be used to directly compare timings between two

points anywhere on the plot. When you bring up the cursors initially you should do so

when the full extent of the plot can be seen.

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Black Box IEEE 1284 Podręcznik Użytkownika Strona 62