Black Box IEEE 1284 Guia do Utilizador descarregar pdf (Página 35)

The Black Box Toolkit Page 35 of 98

8.2.1. Tutorial 1: Measuring synchrony between visual and auditory stimulus

presentation

In order to measure synchrony between visual and auditory stimulus materials you will

need to make use of one or more BBTK Digital Microphones [optional extra]. For this

tutorial detectors are plugged into the following lines on the BBTK:

• line 1: BBTK Digital Microphone

• line 3: Opto-detector

The paradigm on the remote PC is as follows:

• 800x600 bitmapped stimulus image is displayed until a response is detected

• Audio tone is played for 1000ms

• The tone should be synchronised with the first frame of the visual presentation

• After a response there is a 1000 ms wait period in which feedback is displayed

• Screen resolution is 800x600 at 100Hz

Using DSC we can check the following timings:

• Whether the tone is played for 1000ms

• Whether the bitmap and tone are synchronised

• Whether there is a 1000ms wait period after a response

• Whether the refresh rate is 100Hz

Armed with accurate timing information we can reduce or increase the duration of the

bitmap or tone so that it is displayed for the correct amount of time. We can improve the

synchrony by moving either stimulus onset forward or backward. Remember we will be

detecting both the timing error within the paradigm and also within the hardware being

used to present stimulus materials, e.g. the sound card and speakers.

An overview of the expected experimental sequence is shown below.

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Black Box IEEE 1284 Guia do Utilizador Página 35