diff --git a/alf/networks/critic_networks.py b/alf/networks/critic_networks.py
index 72a910cc2..8a7fe3a62 100644
--- a/alf/networks/critic_networks.py
+++ b/alf/networks/critic_networks.py
@@ -67,10 +67,12 @@ def __init__(self,
                  input_tensor_spec,
                  output_tensor_spec=TensorSpec(()),
                  observation_input_processors=None,
+                 observation_input_preprocessors_ctor=None,
                  observation_preprocessing_combiner=None,
                  observation_conv_layer_params=None,
                  observation_fc_layer_params=None,
                  action_input_processors=None,
+                 action_input_processors_ctor=None,
                  action_preprocessing_combiner=None,
                  action_fc_layer_params=None,
                  observation_action_combiner=None,
@@ -89,6 +91,10 @@ def __init__(self,
             observation_input_preprocessors (nested Network|nn.Module|None): a nest of
                 input preprocessors, each of which will be applied to the
                 corresponding observation input.
+            observation_input_preprocessors_ctor (Callable): if ``observation_input_preprocessors`` 
+                is None and ``observation_input_preprocessors_ctor`` is provided, then
+                ``observation_input_preprocessors`` will be constructed by calling 
+                ``observation_input_preprocessors_ctor(observation_spec)``.
             observation_preprocessing_combiner (NestCombiner): preprocessing called
                 on complex observation inputs.
             observation_conv_layer_params (tuple[tuple]): a tuple of tuples where each
@@ -99,6 +105,10 @@ def __init__(self,
             action_input_processors (nested Network|nn.Module|None): a nest of
                 input preprocessors, each of which will be applied to the
                 corresponding action input.
+            action_input_processors_ctor (Callable): if ``action_input_processors``
+                is None and ``action_input_processors_ctor`` is provided, then
+                ``action_input_processors`` will be constructed by calling
+                ``action_input_processors_ctor(action_spec)``.
             action_preprocessing_combiner (NestCombiner): preprocessing called
                 to combine complex action inputs.
             action_fc_layer_params (tuple[int]): a tuple of integers representing
@@ -135,6 +145,7 @@ def __init__(self,
         obs_encoder = EncodingNetwork(
             observation_spec,
             input_preprocessors=observation_input_processors,
+            input_preprocessors_ctor=observation_input_preprocessors_ctor,
             preprocessing_combiner=observation_preprocessing_combiner,
             conv_layer_params=observation_conv_layer_params,
             fc_layer_params=observation_fc_layer_params,
@@ -149,6 +160,7 @@ def __init__(self,
         action_encoder = EncodingNetwork(
             action_spec,
             input_preprocessors=action_input_processors,
+            input_preprocessors_ctor=action_input_processors_ctor,
             preprocessing_combiner=action_preprocessing_combiner,
             fc_layer_params=action_fc_layer_params,
             activation=activation,