final fixes

projects/project_populationvector/populationvector.tex

@@ -36,10 +36,10 @@
   respond to bars in dependence on their orientation.
 
   How is the orientation of a bar encoded by the activity of a
-  population of orientation sensisitive neurons?
+  population of orientation sensitive neurons?
 
   In an electrophysiological experiment, 6 neurons have been recorded
-  simultaneously. First, the tuning of these neurons was characteried
+  simultaneously. First, the tuning of these neurons was characterized
   by presenting them bars in a range of 12 orientation angles. Each
   orientation was presented 50 times. Each of the \texttt{unit*.mat}
   files contains the responses of one of the neurons. In there,
@@ -76,14 +76,24 @@
     gain factor that sets the maximum firing rate.
 
     \part How can the orientation angle of the presented bar be read
-    out from the population activity of the 6 neurons? One is the so
-    called ``population vector''. Think of another (simpler) method.
+    out from one trial of the population activity of the 6 neurons?
+    One is the so called ``population vector'' where unit vectors
+    pointing into the direction of the maximum response of each neuron
+    are weighted by their firing rate. The stimulus orientation is
+    then the direction of the averaged vectors.  
 
-    Load one of the \texttt{population*.mat} files, illustrate the data,
-    and estimate the orientation angle of the bar by two different methods.
+    Think of another (simpler) method how the orientation of the bar
+    may be approximately read out from the population.
+
+    Load one of the \texttt{population*.mat} files, illustrate the
+    data, and estimate the orientation angle of the bar by the two
+    different methods.
 
     \part Compare, illustrate and discuss the performance of your two
-    decoding methods.
+    decoding methods by using all of the recorded responses (all
+    \texttt{population*.mat} files). How exactly is the orientation of
+    the bar encoded? How robust is the estimate of the orientation
+    from trial to trial?
   \end{parts}
 \end{questions}