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HOW TO STUDY SUBLIMINAL RADIO ADVERTISING
--o--
How to Measure Responses to Audio Tape Stimuli

Robert S. Owen, CET, Ph.D.
rsowen@sykronix.com
www.sykronix.com/papers/

Do people really have a left brain and a right brain?  Think about it how is that most people are right handed, some are left handed, and few are equally good at using both hands.  We really do have a left brain and a right brain, or at least a left and a right hemisphere.  Each hemisphere is more suited to some tasks than others, and they communicate with each other through a bundle of wires called the corpus callosum.  If the corpus callosum is cut, interesting things will happen.  If one eye is covered and the person reads a joke, s/he might laugh, yet be unable to explain what was just read and why it was funny.

So what happens if someone is wearing stereo headphones, and we put certain kinds of information into one ear, and other kinds of information into the other ear?  Is it possible for a stereo radio advertiser to plant information directly into one hemisphere without the other figuring out that it was done? 

How To Do It

Below is the "owner's manual" that was written for a project that was used by Dr. Alice Isen, a social psychologist who is known for her studies on affect (feelings).  In this series of experiments, subjects (up to five per session) were seated individually in separate rooms, each equipped with headphones and a hand-held button switch.  Different audio information was presented through the headphones to each ear of all subjects.  Of interest was hemispherical differences in how information was attended, processed and interpreted (right-brain, left-brain stuff). 

In one study, subjects were presented with an affect laden word in one ear and a non-affective word in the other.  Subjects were asked to focus attention on one ear, but to press a thumb button switch if they noticed certain types of words in the other.  Whenever a subject pressed a thumb button, a computer recorded the subject identification (which button was depressed) and the time location on the audio tape that was playing these stimuli. 

The original manual to the equipment set up is below; the programs with hand-written comments will be included as image scans if I get the time to scan them.  Although there might now be easier ways to generate the stimuli described here, the methods described here were state of the art in the early 1980s and would still be reasonable methods to use.
 


DICHOTIC/AFFECT
April 1984
Behavioral Sciences Lab
Ohio State University

Robert S. Owen
 

OVERVIEW

     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 by entering:

          LOAD "DICH*",8  (return)

After loading, type:

          RUN (return)

The computer will display "PROCESSING . . . " for a moment.  It will then prompt:

          CONDITION

The experimenter should ener a unique condition code, such as:

          NAFF10 (return)

The computer will then prompt:

          DATE

The experimenter should then enter the date.  The data file on the disk will then be titled with these two entries separated by aslash.  For example:

          NAF10/12APR84

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 daily.
 

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 1    TRACK 2    TRACK 3    TRACK 4
          tick
          tick
          tick
          tick       one
          tick
          tick
          tick
          tick       two
          tick
          tick
          tick
          tick       ready
          tick
          tick
          tick
          tick       go
          tick
          tick
          tick
          tick                  (word)     (word)
          tick
          tick
          tick
          tick                  (word)     (word)
          etc.                  (etc.)     (etc.)
 

I/O

     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 circuit.)
 

THE PROGRAM

     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, Rockwell, etc.).

     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 needed.

     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).