diff --git a/projects/project_photoreceptor/photoreceptor.tex b/projects/project_photoreceptor/photoreceptor.tex
index bebfbb7..e80b8bb 100644
--- a/projects/project_photoreceptor/photoreceptor.tex
+++ b/projects/project_photoreceptor/photoreceptor.tex
@@ -11,11 +11,16 @@
 
 
 %%%%%%%%%%%%%% Questions %%%%%%%%%%%%%%%%%%%%%%%%%
-\section*{Analysis of insect photoreceptor data.}
+\section*{Light responses of an insect photoreceptor.}
 In this project you will analyse data from intracellular recordings of
-a fly R\.1--6 photoreceptor. The membrane potential of the
-photoreceptor was recorded while the cell was stimulated with a
-light stimulus.
+a fly R\,1--6 photoreceptor. These cells show graded membrane
+potential changes in response to a light stimulus. The membrane
+potential of the photoreceptor was recorded while the cell was
+stimulated with a light stimulus. Intracellular recordings often
+suffer from drifts in the resting potential. This leads to a large
+variability in the responses which is technical and not a cellular
+property. To compensate for such drifts trials are aligned to the
+resting potential before stimulus onset.
 
 \begin{questions}
   \question{} The accompanying dataset (photoreceptor\_data.zip)
@@ -24,22 +29,28 @@ light stimulus.
   \textit{voltage} a matrix with the recorded membrane potential from
   10 consecutive trials, (ii) \textit{time} a matrix with the
   time-axis for each trial, and (iii) \textit{trace\_meta} a structure
-  that stores several metadata. This is the place where you find the
-  \emph{amplitude}, that is the voltage that drives the light
-  stimulus, i.e. the light-intensity.
-  
+  that stores several metadata including the \emph{amplitude} value
+  that is the voltage used to drive the light stimulus. (Note that
+  this voltage is only a proxy for the true light intensity. Twice the
+  voltage does not lead to twice the light intensity. Within this
+  project, however, you can treat it as if it was the intensity.)
+
   \begin{parts}
-    \part{} Create a plot of the raw data. Plot the average response as
-    a function of time. This plot should also show the
-    across-trial variability.\\[0.5ex]
+    \part{} Create a plot of the raw data. For each light intensity plot the average response 
+    as a function of time. This plot should also depict the across-trial
+    variability in an appropriate way.\\[0.5ex]
     \part{} You will notice that the responses have three main parts, a
     pre-stimulus phase, the phase in which the light was on, and
     finally a post-stimulus phase. Create an characteristic curve that
     plots the response strength as a function of the stimulus
     intensity for the ``onset'' and the ``steady state''
-    phases.\\[0.5ex]
-    \part{} The light switches on at time zero. Estimate the delay between stimulus.\\[0.5ex]
-    \part{} You may also decide to analyze the post-stimulus response in some
+    phases of the light response.\\[0.5ex]
+    \part{} The light switches on at time zero. Estimate the delay between stimulus and response.\\[0.5ex]
+    \part{} Analyze the across trial variability in the ``onset'' and ``steady state''. Check for statistically significant differences.
+    \pate{} The membrane potential shows some fluctuations (noise)
+    compare the noise before stimulus onset and in the steady state
+    phase of the response.
+    \part{} (optional) You may also analyze the post-stimulus response in some
     more detail.
   \end{parts}
 \end{questions}