Changing directions with rotary encoder

amk22

Hi,

I'm trying to use the Rotary Encoder module during a lever press behavior. In this experiment, the lever starts at position 0 and needs to remain in the home period for a pre-determined amount of time, then pressed forward to a sound threshold, then continue forward to an apex threshold. Then the lever must be pulled back to the home position to trigger the start of the next trial. For some reason, after the lever reaches the apex threshold, it resets to the lever period of a new trial. I think there's an issue with the state machine recognizing that the lever must change directions, but I can't figure out why my thresholds do not work

Here are the advanced threshold values
RotaryEncoder1_1 = 0-3 (lever must remain here during a wait time)
RotaryEncoder1_2 = 20 (plays sound here)
RotaryEncoder1_3 = 40 (point where lever must reach to return home)
RotaryEncoder1_4 = 0 (lever must be brought back home to trigger a new trial - this is the part that does not work)

Here is the state machine code:
`sma = AddState(sma, 'Name', 'TrialStartTrigger',...
'Timer', 0,...
'StateChangeConditions', {'Tup', 'ResetThresholds'},...
'OutputActions', {'RotaryEncoder1', ['#' 0]}); % timestamp a new trial

sma = AddState(sma, 'Name', 'ResetThresholds',...
    'Timer', 0,...
    'StateChangeConditions', {'Tup', 'WaitPeriod'},...
    'OutputActions', {'RotaryEncoder1', '*E'}); % reset all thresholds based on whether gui was updated and enable

sma = AddState(sma, 'Name', 'WaitPeriod',...
    'Timer', S.GUI.LeverStillPeriod,...
    'StateChangeConditions', {'Tup', 'LeverInit'},... % for testing purposes will always observe the wait period
    'OutputActions', {});


sma = AddState(sma, 'Name', 'LeverInit',... 
    'Timer', 0,...
    'StateChangeConditions', {'RotaryEncoder1_1', 'PressLever'},...
    'OutputActions', {'RotaryEncoder1', [';' 1]});

sma = AddState(sma, 'Name', 'PressLever',...
    'Timer', 2,... % once the lever starts moving, they should do this in a timely manner
    'StateChangeConditions', {'RotaryEncoder1_2', 'DeliverStimulus'},...  
    'OutputActions', {'RotaryEncoder1', [';' 2]});

sma = AddState(sma, 'Name', 'DeliverStimulus',...
    'Timer', S.GUI.SoundDuration,...
    'StateChangeConditions', {'Tup', 'ReturnThreshold'},... % keep pressing forward to the return threshold 
    'OutputActions', {'SoftCode', 1, 'BNCState', 1});

sma = AddState(sma, 'Name', 'ReturnThreshold',...
    'Timer', 2,... % arbitrary to help with smooth movement
    'StateChangeConditions', {'RotaryEncoder1_3', 'DeliverThreshStimulus'},...
    'OutputActions', {'RotaryEncoder1', [';' 4],}); 

sma = AddState(sma, 'Name', 'DeliverThreshStimulus',...
    'Timer', S.GUI.SoundDuration,... 
    'StateChangeConditions', {'Tup', 'PullBack'},...
    'OutputActions', {'SoftCode', 1, 'BNCState', 1}); % play sound here just for testing

sma = AddState(sma, 'Name', 'PullBack',...
        'Timer', 2,...% must do this in a reasonable amount of time to actually get reward
        'StateChangeConditions', {'RotaryEncoder1_4', 'TransitionToNext', 'Tup', 'PullBack'},...
        'OutputActions', {'RotaryEncoder1',[';' 8]});
        
sma = AddState(sma, 'Name', 'TransitionToNext',...
        'Timer', 0,...
        'StateChangeConditions', {'Tup', 'Exit'},...
        'OutputActions', {});
    `

Any advice you have would be greatly appreciated!

Thanks!
amk22

Josh

Hello amk22,

Thresholds are absolute positions, and in the current implementation, zero is considered a positive value. If a threshold set to 0 is enabled while the position is >0, the threshold will be instantly crossed, generating an event.

In your application, you may be able to get around this by setting your home position to a slight negative value (e.g. -1). In bipolar mode (default), negative thresholds must be exceeded in the negative direction.

-Josh

amk22

Hi Josh,

Thank you! This helps a lot. I didn't realize that if the lever were already past the threshold when it is enabled that it would be instantly crossed. I thought that the thresholds would be able to be crossed in multiple directions. Is there a way to go back and forth across thresholds for potentially more complicated protocols? For the home position, I will try setting it to negative values so it can cross in the negative direction.

Thanks again,
amk22

Josh

Hello amk22,

Good point! I added this to the Bpod dev stack for a future update. It would definitely be useful to have a mode where threshold direction is automatically set on threshold-enable.

-Josh