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[CV]

Psycho acoustic setup

Below is shown a video of a hooded crow subject operating the panel in the psycho acoustic setup (move the mouse over the video to start it). The procedure is a yes/no procedure and the method of constant stimuli.

 

Alternatively: open the video in your default player here.

The crow initiates a single trial by pressing the middle button with the red LED. Then either a tone of a certain level or no tone is played back. The crow must then "answer" whether it thinks there is a tone or not. The crow answers "yes" by pressing the right button and "no" by pressing the left.

The video shows three trials:

1) In the first is a "no tone" trial and the crow answers correctly "no" by pressing the left button. This is called "correct rejection" (CR). Two correct answers in a row is food rewarded. This is the first correct answer and no food pellet is yet given but as a secondary reinforcer the machinery of the food pellet automate runs. If the crow is food rewarded every time the task is too easy and the crow is not as concentrated on listening after the tones (i.e. it is not so much under stimulus control).

2) The second trial is a "tone trial" and you should also be able to hear a tone on the video. The crow answers correctly "yes" by pressing the right button, which is called a "HIT". This is the second correct answer in a row and the crow is rewarded by a food pellet.

3) The third and last trial is also a tone trial but the tone is very faint and the crow doesn't hear it. Thus the crow answers "no" in good faith. This is nevertheless wrong, and called a "MISS", and the crow is "punished" by cage illumination blackout. This punishment is very mild, since the crows are not afraid of the dark, but gets a bit frustrated that they are not able to work for the food.

One may ask why punish a poor crow who does not have a chance to hear the faint sounds? Well first, we don't know what the crow can hear and not hear and this is what we wish to find out by it's yes and no answers and to establish its threshold we need to go below it. Secondly, if there were no punishments the game would be too easy and the crow would not care much if it answers correct or not since it would get a reward sooner or later with no costs! Thus to keep the crows under "stimuli control" as it is called, punishment is necessary.

The video showed three different outcomes of the crows yes/no answers in the three trials: CR, HIT, and MISS. There is a fourth outcome: if the crow answers "yes" because it thought it heard a very faint sound, but there were in fact no sound, it has made a false alarm (FA).

Thus there are four different outcomes. By performing statistics on the proportions of these four outcomes in a series of trials (a session) one can calculate the threshold.