Software: Use of another computer to deliver stimuli.
This method of stimulus generation allows a computer or other device to deliver stimuli, with a hook up to the PSYLAB measuring system so that crucial event 'cues' are registered at the precise time they occur, allowing physiology to be later analyzed relative to these stimuli.
There are a number of computer programs that may be used to present a stimulus task to the subject, including a system known as MEL. Graphic generations programs, sound generation programs, mixed media devices, on both Macintosh and PC computers. In the case of mixed media tools, a way must be found of determining the precise moment when the stimulus is delivered. These type of programs generally have unpredictable delays due to the complexity of the programs and the multi-tasking operating system. PSYLAB provides unique tools for determining precise stimulus timing in these circumstances - please contact CPI for specific information relating to your particular requirements.
As well as multi-media and MEL, Quick BASIC or PASCAL may be used to program a task An example of the type of task that has been generated in this way is one where the subject reads a word from the compuetr screen and responds by pressing a key. The compueter might be programmed to measure the subject's reaction time in addition to correct or incorrect response.
All that is required from the point-of-view of the hook-up to the PSYLAB system is that the task program sends a value to the printer port to indicate the occurrence of the event. The port registers one byte, a value between 0 and 255. Any value above zero may be used to indicate different categories of event - PSYLAB will be able to sort events using this category when data are analyzed. Th printer port may be accessed with a program 'poke', or the appropriate instruction in MEL etc. The physiscal address of the printer port is 888 (decimal), so in Quick BASIC the instruction 'OUT X,888', where X is the event category, is all that is required.
A BIN8, Binary Input / Output device is required in the PSYLAB system This provides 8 TTL (a standard electronic system for representing 1 or 0 as a voltage, where 1 is high or about 3V and 0 is low or about 0.8V) inputs and 8 TTL outputs. The inputs may be registered in PSYLAB by adding a 'STIMIN' type event channel. A cable can be supplied which allows the BIN8 to be plugged directtly to the printer port.
PSYLAB measures selected physiology from the appropriate measuring amplifiers and transducers, using either continuous or circular measurement methods. The circular buffer method is where PSYLAB continuously registers data from the amplifiers, but only records it when the event occurs. It is called circular because the measures are temporarily stored in a repeating buffer, so that it is possible to store data which occured before the stimulus was registered.
Events are registered in a channel parallel with physiology data, so that it can be seen when visually examining the record that blocks of data are correctly synchronised with the stimulus. Blocks are then analyzed using PSYLAB5 tools, as described in the various analysis examples here.
An example of a block of data recorded relative to an external stimuls event, seen in the lower blue channel.