Low Contrast Test
#253500

The ability to detect objects of low contrast is an important component of the visual system. Determining the levels of contrast that an infant can detect, helps planning information for intervention and provides a baseline to evaluate future changes. Deviations from usual behavior may indicate disorders that leave vision at high contrast levels unaffected.

Hiding Heidi test is designed for measurement of contrast sensitivity in infants, children and adult persons who are unable to respond verbally or by pointing. If the infant/person can follow a moving target or shift gaze to or turn head to peripherally presented visual stimuli, preferential looking test situations can be used. A preferential looking test situation is a detection test and does not depict how the infant/ child perceives the test picture. However, if an infant responds with a smile, he must have perceived the picture of a smiling face.

The test picture is exposed from behind the white card by moving the cards in opposite directions with the same speed. The normal reaction is that a young infant follows the picture of the face with a combined movement of the eyes and head (the differentiation of eye movements from head movements has not yet developed). If the infant follows the card and smiles like this infant does, he must have perceived the smiling face and responds with a age appropriate social smile. In the brief moment of the test you have received information on the infant’s visual, motor and emotional development.

Since the picture of the face has such high interest value for young infants, the low contrast Hiding Heidi pictures can be used to assess perception of low contrast large forms long before recognition of forms can be measured. The prerequisite for an age appropriate response is that the infant has the function of the mirror cell networks.

Even though "infant" is referenced in the following instructions, the directions also apply for young children and multihandicapped people.

1. Position the infant so he or she faces the examiner and in the optimal position for best visual performance. Support his or her head so involuntary motor movements least affect the infant's performance. The infant can look over the parent's shoulder while being held, sit in their lap or in the child's buggy. If possible, select for the first assessment the best time of day when the infant is most alert.
   
   

2. Before observation of the infant's responses to the faces, familiarize yourself with the infant's usual response pattern and look for: the head turning toward an interesting visual object, eye widening, breathing, quieting, eyebrow arching, smiling, babbling to or reaching for an object.
   
   

3. During your communication with the infant, notice how far you can back away from the infant without losing his or her attention to your face. Record this distance, so you can later document changes in the infant's visual sphere. Test within this visual space or ”sphare for visual communication”.
   
   

   

4. Hide the stimulus card behind the blank card. Then ask the child "Where is Heidi hiding?", while moving the blank card off to one side and the stimulus card off to the other side at the same speed. Stimulus cards should be moved to the right and/or left in a random order.

   The cards are presented in the order of decreasing contrast 100%, 25%, 10%, 5%, 2.5% and 1.25%. When the infant does not follow the movement of the face picture, place the picture behind the white card and say ”Heidi is hiding now”, tap on the white card wih your fingers and then present the picture again. If you do not see the usual response, go to the previous contrast to confirm the threshold level. Record it and the testing distance used. When you have tested the next test, you might briefly test the threshold card and the lower contrast cards at a shorter distance to see, whether the distance played a role.

   The tester may notice that an infant does not follow the movement of the Heidi-picture with eye move-ments or with combined eye-head movements but makes a quick shift of gaze to the picture when it stops. Another child may follow the movement but looks puzzled when the movement stops and looks at the tester as if asking "Where did the picture disappear to?" These observations need to be reported to the child’s neurologist because they may mean that the child has problems in motion perception (= perception of movement or perception of objects that stand still).

   If an infant does not respond to a horizontal presentation of the face cards use a vertical presentation.