comparison Copy_of_multithreshold 1.46/Levitt2.m @ 28:02aa9826efe0

mainly multiThreshold

+function [nextStep, msg]=Levitt2 (decision, currentValue)
+global LevittControl withinRuns
+% descision is a string: 'hit' or 'miss'
+% current value is the value of the variable parameter (e.g. level)
+% msg:
+%     msg='' indicates trial progressing successfully
+%     msg='done' indicates that a threshold estimate has been found
+%     msg='maximum level exceeded'
+%     msg='maximum no of trials exceeded'
+
+% Initialize by running Levitt2 without arguments
+%  later LevittControl will be set in aReadAndCheckParameterBoxes in  expGUI_MT
+if nargin==0
+    
+    LevittControl.peakTroughValues=[];   
+    LevittControl.trialRunning=0;
+    LevittControl.sequence='****'; 
+    LevittControl.LevittValuesUsed=[NaN NaN NaN NaN];
+    LevittControl.TurnsToSmallSteps=4; % 2 peaks and 2 troughs
+    LevittControl.direction='same';
+    LevittControl.prevDirection='easier';
+    LevittControl.Nreversals=0;
+    
+    LevittControl.trialRunning=1;
+    LevittControl.meanPeakTrough=NaN;
+    LevittControl.sd=NaN;
+    msg='';
+    return
+end
+
+% apply Levitt rules to find next stimulus value
+rule=LevittControl.rule;
+sequence=LevittControl.sequence;
+meanPT=LevittControl.meanPeakTrough;
+sdPT=LevittControl.sd;
+
+% response sequence: '+' is a hit and '-' is a miss.
+if strcmp(decision,'hit')
+    sequence=[sequence '+'];
+else
+    sequence=[sequence '-'];
+end
+LevittControl.LevittValuesUsed=[LevittControl.LevittValuesUsed withinRuns.levelList(end)];
+
+switch rule
+    case '++'
+        peakCriterion='-++';
+        troughCriteria={'++ -', '++ +-'};
+    case '+++'
+        peakCriterion='-+++';
+        troughCriteria={'+++ -', '+++ +-', '+++ ++-'};
+    otherwise
+        error('Levitt:')
+end	
+
+troughs=[]; allTroughPtrs=[];
+for i=1:length(troughCriteria)              % do all trough criteria
+    troughCriterion=char(troughCriteria(i));% one criterion at a time
+    % identify the location of a trough
+    troughPtrs=findstr(sequence, troughCriterion) + length(troughCriterion)-1;
+    % identify the level at which it occurred
+    troughLevels=LevittControl.LevittValuesUsed(troughPtrs);
+    % archive the list
+    withinRuns.troughs=troughLevels;
+    troughs=[troughs troughLevels];
+    allTroughPtrs=[allTroughPtrs troughPtrs];
+end
+% only one peak criterion used
+withinRuns.troughs=troughs;
+peakPtrs=findstr(sequence,peakCriterion)+length(peakCriterion)-1;
+peakLevels=LevittControl.LevittValuesUsed(peakPtrs);
+withinRuns.peaks=peakLevels;
+
+% almagamate and sort into date order
+peakTroughList=[peakLevels troughs];
+peakTroughPtrs=[peakPtrs allTroughPtrs];
+[peakTroughPtrs idx]=sort(peakTroughPtrs);
+% it needs to be sequenced so that the algorithm can take the last peaks
+% and troughs
+peakTroughList=peakTroughList(idx);
+
+% adjust step size as the trial progresses
+% a positive step size indicates the 'harder' direction 
+if length(peakTroughList)>=LevittControl.TurnsToSmallSteps
+    currentStep=LevittControl.steadyLevittStep;
+else
+    currentStep=LevittControl.startLevelStep;
+end    
+
+% base next stimulus on the basis of the sequence
+%  any miss requires an 'easier' stimulus next time.
+if strcmp(sequence(end),'-')
+    nextStep= -currentStep;
+    
+    % success requires 2 or more successive hits
+elseif strcmp(sequence(end-length(rule)+1:end),rule)
+    sequence=[sequence ' '];  % add space to prevent success on successive trials
+    LevittControl.LevittValuesUsed=[LevittControl.LevittValuesUsed NaN];
+    nextStep=currentStep;
+    
+    % not enough hits to provoke a change
+else	
+    nextStep=0;
+end
+
+LevittControl.sequence=sequence;
+
+LevittControl.Nreversals=length(peakTroughList);
+% compute threshold estimate 
+% only if minReversals exceeded and even number of peaks and troughs
+if LevittControl.Nreversals>=LevittControl.minReversals && rem(length(peakTroughList),2)==0   
+    % use only the peaks and troughs at the end of the sequence
+    peaksAndTroughs=peakTroughList(end-LevittControl.useLastNturns+1:end);
+    disp(['peak/trough sequence= ' num2str(peaksAndTroughs, '%6.0f') ] )
+    
+    meanPT=mean(peaksAndTroughs);
+    sdPT=std(peaksAndTroughs);
+    LevittControl.meanPeakTrough=meanPT;
+    LevittControl.sd=sdPT;
+    fprintf('Levitt, mean, sd= %6.1f,%6.1f\n', meanPT, sdPT)
+    % final check that the sd is low enough
+    if sdPT<LevittControl.targetsdPT        
+        nextValue=currentValue;
+        msg='done';
+        return
+    end
+end
+
+nextValue=currentValue + nextStep;
+if nextValue>LevittControl.maxLevittValue
+    msg='maximum level exceeded'
+    return
+end
+
+% required for later use
+LevittControl.trialRunning=LevittControl.trialRunning+1;
+LevittControl.peakTroughValues=peakTroughList;
+
+if LevittControl.trialRunning>LevittControl.maxTrials
+    msg='maximum no of trials exceeded'
+    return
+end
+
+% Trial continues
+msg='';