Add SPARC reference documentation and remove redundant validator comments

Author: sanketsabharwal

pyeyesweb/mid_level/smoothness.py

@@ -26,6 +26,12 @@ class Smoothness:
     and Jerk RMS metrics. It can optionally apply Savitzky-Golay filtering
     to reduce noise before analysis.
 
+    SPARC implementation is based on Balasubramanian et al. (2015) "On the analysis
+    of movement smoothness" from Journal of NeuroEngineering and Rehabilitation.
+    SPARC values are typically negative, with values closer to 0 indicating less
+    smooth movements. Healthy reaching movements typically yield SPARC values around
+    -1.4 to -1.6, while pathological movements may range from -3 to -10 or lower.
+
     Read more in the [User Guide](/PyEyesWeb/user_guide/theoretical_framework/low_level/smoothness/)
 
     Parameters
@@ -62,13 +68,16 @@ class Smoothness:
     1. SPARC: More negative values indicate smoother movement
     2. Jerk RMS: Lower values indicate smoother movement
     3. Requires at least 5 samples for meaningful analysis
+
+    References
+    ----------
+    Balasubramanian, S., Melendez-Calderon, A., Roby-Brami, A., & Burdet, E. (2015).
+    On the analysis of movement smoothness. Journal of NeuroEngineering and Rehabilitation,
+    12(1), 1-11.
     """
 
     def __init__(self, rate_hz=50.0, use_filter=True):
-        # Validate rate_hz using centralized validator
         self.rate_hz = validate_numeric(rate_hz, 'rate_hz', min_val=0.01, max_val=100000)
-
-        # Validate use_filter using centralized validator
         self.use_filter = validate_boolean(use_filter, 'use_filter')
 
     def _filter_signal(self, signal):