Subject: Re: Instruction for subjects From: Al Bregman <bregman(at)HEBB.PSYCH.MCGILL.CA> Date: Tue, 25 Oct 2005 22:35:25 -0400Dear Fatima and List, One way to deal with the fact that only one of the sounds to be compared has a noise burst in the middle while the other has not, is to make BOTH sounds in the comparison have a noise burst. One sound would be the one you described -- an FM sweep with a white noise burst (WNB) replacing the gap. The one with which it is to be compared could also have a noise burst in the middle, but one that doesn't produce continuity. This can be accomplished if the noise is a notched-noise burst (NNB). The NNB can be made as loud as the WNB, but it shouldn't have any frequencies at or near the frequency of the tone glide at its midpoint. Of course the effects of higher and particularly lower frequencies in the NNB will spread; so you will have to do some preliminary listening to discover how wide the notch has to be in NNB in order not to induce continuity. The subjects can then be told to ignore the noise bursts (which may not sound the same) in both sounds, and to judge only the tone glides. You might consider having the following conditions: 1. Actually-continuous glide passing through WNB. 2. Glide with gap filled by WNB (auditory induction condition) 3. Actually-continuous glide passing through NNB 4. Glide with gap filled by NNB. The percepts resulting from these conditions should be: 1. Continuous glide 2. Continuous glide 3. Continuous glide 4. Discontinuous glide (verification of the fact that NNB doesn't produce continuity) Any differences between the sounds of 1, 2, and 3 would be very interesting. If condition 2 is not actually producing continuity (according to your own ears), you might try: -- A shorter gap -- Having, as the stimulus, a series of connected ascending and descending glides, with the gaps (or noise) placed in the middle of each ascending and each descending glide. This repetition may favor continuity. Another change you might consider is in the question you ask. If there are two sounds to be compared, S1 and S2, you might say: "Ignore the noises and focus only on the tones. Which tone has a longer gap in it, the first or the second. If Condition 4, above, really sounds discontinuous, it could be used as S1, but you could change the duration of the gap on different trials (keeping the duration of the noise constant). In this way you could calibrate the size of any induction effects, even if they only shortened the apparent length of the gap, rather than eliminating it altogether. Dick Warren has a lot of experience in these types of experiment and much of what I have proposed is based on his findings. You might want to consult him directly. I'm sorry, but I don't have his current e-mail address. Maybe other list members do. Dick, are you out there? Best of luck, Al ---------------------------------------------------- Albert S. Bregman, FRSC Emeritus Professor Psychology Dept., McGill University 1205 Docteur Penfield Avenue Montreal, Quebec Canada H3A 1B1 Voice & Fax: +1 (514) 484-2592 ---------------------------------------------------- ----- Original Message ----- From: "FATIMA HUSAIN" <fthusain(at)HELIX.NIH.GOV> To: <AUDITORY(at)LISTS.MCGILL.CA> Sent: Tuesday, October 25, 2005 1:42 PM Subject: Instruction for subjects > Dear List > > I am running some pilot behavioral studies of auditory continuity illusion > (aka temporal induction). > The sounds are FM sweeps with gaps or noise-inserted gaps. > For various reasons I am running them as "same/different" trials, wth the > first sound of the trial being a regular FM sweep and the second one being > the modified FM sweep. > > When I ask the subjects, "Is the second sound as continuous as the first > sound?" they become confused. > > Even FM sweeps with much-louder noise inserted in the gap are considered > by some subjects to be not very continuous. (contrary to literature) > > How do I change my instructions (basically, the confusion is around the > word 'continuous')? Or change the task? > > Any ideas? > > Thanks > > Fatima T. Husain, Ph.D. > NIDCD/NIH > Bldg. 10/ Room 8S-235D > Phone: 301-594-7758 > >