Effects of arm weight on C-not-B task performance: implications for the motor inhibitory deficit account of search failures.

Toddlers have been found to fail on a three-location search task involving the invisible displacements of an object, namely the C-not-B task. In this task, a child is shown the experimenter's hand that contains a toy. The toy then successively disappears under the three cloths (A, B, then C). The examiner silently releases the toy under the second cloth (B). The hidden object makes a bump in the B cloth that covers it. Young children emit a strong bias toward the last cloth that the experimenter's hand passes under, and this has been labeled the C-not-B error. One possible explanation for toddlers' failures in the C-not-B task is that children lack the motor inhibitory mechanisms. To test this hypothesis, the robustness of the C-not-B error was tested, in a first experiment, against variations in body parameters. By putting additional weights on the arm, the C-not-B error was reduced substantially and the C-not-B task had a higher rate of success. Indeed, in contrast to control participants, who ignored a visual clue indicating the correct location of the hidden object and reached for the last location of the experimenter's hand, the participants with arm weights initiated their reaching movements by using the visual clue. The findings from the second control group indicate that the dramatic increase in successful performance by children with arm weights is not merely a consequence of the focus on the attention to arm movements. The motion of the experimenter's hand in space appears to have made the task difficult because toddlers had no problems inferring that a lump under a cloth indicates the existence of an object without actually having watched an object be hidden there, as demonstrated in a second experiment. The findings are consistent with the hypothesis that C-not-B task content activates a prepotent motor response that preempts full consideration of a visual clue indicating the correct location of the hidden object. We propose that the success in the C-not-B task of toddlers with additional arm weights could result from a disruption of automatic hand movement that is triggered by sensory signals, namely salient features of the C-not-B task.

The use of perspective as a depth cue with a 2D display in 4 and 5-month-old infants.

Four experiments were conducted to study the use of perspective as a depth cue in infants, using an eye-tracking-system. In the first experiment, no significant difference was observed between the looks for the "normal" and the "strange" events on the complete display and at the target in 4-month-olds. In the second experiment, the results of 5-month-olds were similar to those obtained by 4-month-olds but they looked more at the test events when the "strange" event was presented first. In the third experiment, 5 month-olds were shown a repeated presentation adapted from the "Partial-Lag" design. Infants' exploration of the target indicated that they looked more at the "strange" event than at the "normal" event. In the fourth experiment, the same design was used with 4-month-olds but no difference between conditions was observed. Five-month-olds seem to be able to use the perspective cues alone. These different data are discussed.

Qualitative differences in the exploration of upright and upside-down faces in four-month-old infants: an eye-movement study.

Four-month-old infants were habituated with an upright or an upside-down face. Eye-movement recordings showed that the upright and upside-down faces were not explored the same way. Infants spent more time exploring internal features, mainly in the region of the nose and mouth, when the face was upright. They also alternated as frequently between the face's internal features (eyes vs. nose/mouth) as between external and internal features. When the face was upside down, the infants spent half of their time exploring external features, and preferentially alternated between external features and internal features. The main effect of inversion was a decrease of the looking time to the nose/mouth region and of the number of shifts between the eye region and the nose/mouth region.

Spatial cognition in young children with spinal muscular atrophy.

Success in visuospatial tasks has often been demonstrated in teenagers with spinal muscular atrophy (SMA). However, what has been tested in these studies, with the Wechsler Intelligence Scale for Children-Revised (Wechsler, 1974) performance scale, does not deal with the spatial capacities that co-occur with the advent of self-produced locomotion. Indeed, various studies have shown that occurrence of locomotion in infancy is correlated with the development of visuospatial cognitive competencies, suggesting that locomotor experience might play a central role in spatial development, especially in the realm of manual search for hidden objects. It is thus of interest to assess spatial search skills in SMA young children suffering total deprivation of locomotor experience. Twelve Type-2 SMA children with a mean age of 30 months were compared with controls with respect to their spatial search skills in a memory-for-locations task. In this search task, hiding containers were rotated 180 degrees before search was permitted. The performance obtained with the SMA group did not differ from that obtained in the healthy control group. SMA patients searched correctly for a hidden object in the 3-choice search task. Locomotor impairment does not appear to be a key risk factor for dramatic slowing down or deviation in the development of spatial search skills, as assumed by some authors. Further research is needed to identify the alternative pathways to normal spatial development that are used by SMA young children.