diff --git a/splearn/spectral.py b/splearn/spectral.py
index f0cddbaa64461ed78525b6fe58e89f296a0b00d5..95ef9902f9bfbe6f11205a07494b581c396dbe9d 100644
--- a/splearn/spectral.py
+++ b/splearn/spectral.py
@@ -571,7 +571,10 @@ class Spectral(BaseEstimator):
 
         - Output:
 
-        :returns: mean of Log Probability corresponding to the input X
+        :returns: mean (resp. sum) of Log Probability corresponding to the input X
+		  if normalize is True (resp. False) and y is None. If y is a vector
+		  of target values, the mean (resp. sum) is calculated over the square
+		  of differences.
         :rtype: float
         """
         warnings.simplefilter("error", RuntimeWarning)
@@ -640,4 +643,4 @@ class Spectral(BaseEstimator):
                         raise ValueError(msg)
                 return perplexity
         else:
-            return - self.loss(X, y, normalize=True)
\ No newline at end of file
+            return - self.loss(X, y, normalize=True)