Behavioral Sciences Lab
Ohio State University
Robert S. Owen
Words spoken from an audio tape are heard
by each of five subjects through headphones. The words spoken into
the left ear are different from those spoken into the right ear.
Each of these word pairs, however, is spoken simultaneously with the other.
These words are also "heard" by the computer.
The subject is instructed to momentarily
press a switch button whenever s/he hears a specific kind of word.
The switch is connected to the computer. Each of the five subjects
is put into a separate room. Each room is equipped with a headphone
set and a hand-held button switch.
The computer saves all data on a floppy
disk. Each time any subject presses a button, the computer saves
the number of the subject pressing the button, the present word number,
and the time interval (in milliseconds) rom the start of the spoken word
to that button press.
RUNNING THE PROGRAM
This program is loaded into the computer
After loading, type:
The computer will display "PROCESSING . . . " for a moment.
It will then prompt:
The experimenter should ener a unique condition code, such as:
The computer will then prompt:
The experimenter should then enter the date. The data file
on the disk will then be titled with these two entries separated by aslash.
Be sure to hit the (return) key after each of these entries.
The computer will now wait for the audio
tape to begin playing. It will automatically open the data file on
he disk and will automatically close the file approcimately 16 seconds
after the tape has stopped.
Five red indicators are displayed on the
screen. These will flash whenever a button is being pressed.
This gives the experimentor an indication that the buttons are all working
properly and that the subjexts are each following instructions properly.
On the right side of the screen is a yellow
volume level indicator. When the audio tape is playing, the indicator
should bounce up when the word is spoken and come back down between words.
Adjust the amplifier volume control so that this indicator bounces past
the top of the screen when a word is spoken and falls about halfway down
between words. Exact adjustment is not critical but should be checked
GENERATING THE STIMULUS TAPE
The tape played to the subjects is an ordinary
audio cassette. The master tape, however, must be generated using
a 4-track tape recorder. Since the words on the left channel must
be spoken simultaneously with those on the right, generating a tape directly
in stereo is not possible.
To assist a human (reading a list of words)
in generating simultaneous recordings, two control tracks are recorded
on the 4-track tape. The first track functions as a metronome, used
exactly as a musician would use a metronome to keep the "beat" as s/he
plays a musical instrument. The metronome signal is generated by
the computer and recorded onto the tape first.
The second control track tells the person
reading the list when to begin. S/he simply records on to this track,
"one . . . two . . . ready . . . go . . ." These two control tracks
are then played back through the headphones while the lists of words are
separately recorded simultaneously on the third and fourth tracks.
These third and fourth tracks are then copied onto an ordinary cassette.
TRACK 2 TRACK 3 TRACK 4
The five push button switches are connected
to the 6526 CIA (U1) through control port 1. They are polled by the
machine code routine starting at mm49400.
The sound is input to the POT X input of
the 6581 SID (U18) through control port 1. The sound signal is isolated
electrically from the computer using a Cds photocell and light bulb.
The sound signal from the tape player is
firstamplified by an amplifier. This amplifier must be capable of
a "monophonic" mode; the left and right channels must be mixed for
proper use with this program. The amplifier speaker output is then
connected directly to the light bulb. NOTE: make sure that DC is
not also being amplified by the amplifier; the tape player might have to
be coupled to the amplifer through a capacitor.
The program reads the input of a new word
by measuring the resistance ofthe photocell. The program also moves
a volume level indicator on the screen for use in making amplifier adjustments.
The photocell/lightbulb arrangement was
chosen for its simplicity. The same sort of isolation could have
been achieved sing a phototransistor/LED combination. This, however,
would have required extra electronics to properly drive the LED: strict
attention would have to be paid to input levels. Also, because of
its fast rise and decay times, more complex programming would have to be
constructed to properly read the phototransistor.
The photocell's natural damping provides
for easy programming. Only the rise in volume level is being read
by this program. Relative, rather than absolute, time measurements
are being made.
(See also the the line level audio
to integrating type ADC circuit and the voice key
The BASIC portion of this program should
need no explanation to anyone familiar with the C-64 computer. The
working portion of the program is run entirely in machine code as contained
in the DATA statements.
The program could not be transferred to
another computer; it makes heavy use of sprite graphics and Kernal system
routines unique to the C-64 computer. The skeleton may be used to
write a new program for use with another 65XX based computer (Apple, Atari,
The working part of the program starts
at mm49152. A subroutine of this at mm49400 polls the buttons for
a press. If any ofthe buttons are pressed, a subroutine at mm49600
saves the data on disk.
Timing is done using the A and B interval
timers of CIA #1. The low byte of timer A is not saved to disk since
only millisecond resolution is needed. The high byte of of timer
B is also not saved since timing over a few hundred milliseconds is not
This program will loop until sound is input.
When the first word enters the computer, the word number, N, is set to
1. It is incremented with each new word. The program will close
out after no sound is received for approximately 16 seconds (timer B rolls
over). Note the use of Kernal routines for machine code access to
he disk (mm49600).