Biomedical subjects

Masami K Yamaguchi

Publications and source records attributed to Masami K Yamaguchi.

10 recordsLinked to original sources

PubMed2006

Neural activation to upright and inverted faces in infants measured by near infrared spectroscopy.

The present study examined infants' brain activity in response to upright and inverted faces using near infrared spectroscopy (NIRS), which can non-invasively record hemodynamic changes of the brain. NIRS is particularly useful for recording in infants, since recordings can be made, even while the infants are awake, without fixing their body and brain. For this objective, we used newly developed sensor probes of NIRS for recording in infants. We measured changes in cerebral oxygenation in 10 5-8-month-olds' left and right lateral areas while they were looking at upright and inverted faces. The results are summarized as follows: (1) the concentration of oxyhemoglobin (oxy-Hb) and total hemoglobin (total-Hb) increased significantly in the right lateral area during the upright face condition, (2) the concentration of total-Hb in the right lateral area differed significantly between the upright and inverted conditions, (3) hemodynamic changes were maximal in the temporal region, probably in the superior temporal sulcus (STS) in both hemispheres, and (4) the right hemisphere seems to be more important for recognizing upright faces. This is the first evidence showing that there is an inter-hemispheric difference on the effect of face inversion in the infant brain using a hemodynamic method.

Face↗

PubMed2006

Development of modal and amodal completion in infants.

Visual completion has been divided into two types: modal and amodal. While psychophysical studies with adults provided several common properties between modal and amodal completion, studies with infants showed differential trends in the development of these perceptual abilities. In the present study, we further examined the development of these two kinds of visual completion in infants aged 3 to 6 months. We created a display composed of a partially overlapping circle and square. The display induced either modal or amodal completion depending on the colour. Infants were familiarised with either the modal or the amodal display. After this familiarisation, the infants were tested on their discrimination between the complete figure and the broken figure. If the infants could perceptually complete the figures in the familiarisation display, they were expected to show a novelty preference for the broken figure. A total of thirty-two infants participated in the present study. Our results suggest that modal completion develops by 3-4 months of age, whereas amodal completion develops by 5-6 months of age.

Child Development↗

PubMed2005

Anisotropic motion coherence sensitivities to expansion/contraction motion in early infancy.

We investigated 2- and 3-month-olds' motion coherence sensitivities to radial expansion/contraction by using the preferential looking method. The infants were tested with a stimulus composed of two dynamic random dot patterns placed side by side: an expansion (or a contraction) pattern and a random directional pattern. The results showed that the 3-month-old infants tested with both a contraction and random directional pattern could discriminate between those two motions significantly, even when the contraction motion coherence was relatively low (50%). On the other hand, the 3-month-old infants who were tested with both expansion and random directional pattern could not discriminate between those two motions. None of the 2-month-old infants showed significant discrimination between the expansion/contraction and random motion patterns. Results of the present study suggest that anisotropic motion coherence sensitivities to radial expansion/contraction emerge at around 3 months of age.

Child Development↗

PubMed2005

Perception of opposite-moving dots in 3- to 5-month-old infants.

We conducted four experiments on the development of motion perception in a total of 109 3- to 5-month-old infants using motion stimuli consisting of opposite-moving dots. A psychophysical study showed that adult subjects perceived two global planes with opposite-moving dots, but this global perception collapsed when paired opposite-moving dots were located within 0.4 deg of one another (Qian, Andersen, & Adelson, 1994). We used this paired-dot stimulus as a non-target and the opponent motion stimulus as a target and examined target preference using methods based on forced-choice-preferential looking (Teller, 1979). In Experiment 1, we used 90 moving dots as stimuli. The results showed that 5-month-old infants had a significant preference for the targets but 4- and 3-month-olds did not. In Experiment 2, we used a small number of dots, and the results showed that 5-month-old infants did not prefer the target significantly. These results suggest that the preference for a target decreases according to the number of dots. In Experiment 3, we used opponent motion with long traveling length of the dots, and the results showed that all age groups, including 3-month-olds, had a preference for the moving targets. We showed that the preference observed in Experiment 3 was dependent not on local traveling length but on the global opponency. These results suggest that the perception of motion opponency based on a global motion cue emerges at 5 months of age (Experiments 1 and 2) and that the traveling length of the dots promote this perception (Experiments 3 and 4).

Child Development↗

PubMed2005

Perception of motion trajectory of object from the moving cast shadow in infants.

A moving cast shadow of the object affects the perception of the object's trajectory in adults [Kersten, D., Mamassian, P., & Knill, D. C. (1997). Moving cast shadow induce apparent motion in depth. Perception, 26, 171-192]. In the present study, we investigated by using a habituation-dishabituation procedure whether infants at 4- to 7-months old discriminate the motion trajectory of a ball from the moving shadow it casts. In Experiment 1, 4- to 5-month-old and 6- to 7-month-old were tested for ability to discriminate between a "depth" display containing a ball and a cast shadow with a diagonal trajectory and an "up" display containing a ball with a diagonal trajectory and a cast shadow with a horizontal trajectory. Six- and 7-month-old, but not 4- and 5-month-old, infants looked significantly longer at the "up" display than at the "depth" display. In Experiment 2, we tested whether 4- to 5-month-old and 6- to 7-month-old infants would perceive "up" motion as categorically different from "depth" depending on the object's 3-D trajectory. We used displays containing a ball and a cast shadow with the same trajectories as those in Experiment 1 except that the cast shadows appeared above the ball. These displays did not produce 3-D impressions in adults. Neither age group of infants exhibited significant differences between "up" and "depth" displays. When the results from the two experiments are considered, 6- and 7-month-old infants discriminated the motion trajectory of the ball from the moving cast shadows. This developmental emergence of depth perception from a moving cast shadow at 6 months of age is consistent with that of other pictorial depth cues.

Aging↗

PubMed2004

Asymmetry in the perception of motion-in-depth.

We investigated the anisotropic responses between the detection of motion toward and motion away from the observers with expanding/contracting shaded circles. Our experiments followed visual search paradigm with two exceptions: (1) the stimulus presentation time was fixed for 300 ms and (2) the mean error rates were adopted as a dependent variable. In Experiment 1, targets and distractors were defined by expanding (or contracting) convex/concave circles. Results of Experiment 1 suggested that the human visual system is more sensitive to expanding convex circles (which create the impression of approaching objects) than others. In Experiment 2, the targets and distractors were defined by expanding (or contracting) step gradient (top-lighting/bottom-lighting) circles. The results of Experiment 2 suggest that the anisotropy for the perception of motion-in-depth should not be caused by change of luminance polarity but by change of shading cue.

Adolescent↗

PubMed2004

Sensitivity to linear-speed-gradient of radial expansion flow in infancy.

A radial expansion flow having a linear-speed-gradient (linear-grad) creates robust perception of a rigid object moving-in-depth [Perception 19 (1990) 21]. It has been reported that sensitivity to a linear-grad of radial expansion emerges at 2 months of age [Infant Behavior and Development 17 (1994) 165]. In the present study, we examined the development of sensitivity to the linear-grad of radial expansion after 2 months of age with three experiments. A total of 197 2- to 5-month-old infants participated. The results showed that sensitivity to the linear-grad improves between 2 and 3 months of age (Experiment 1), and that the infants may discriminate between an expansion having linear-grad and that having zero-grad based on their perception of motion-in-depth (Experiments 2 and 3).

Aging↗

PubMed2004

The effect of support ratio on infants' perception of illusory contours.

We used a preferential looking technique to investigate the effect of support ratio (a ratio of the physically specified contours to the total edge length) on the perception of Kanizsa illusory contours in infants aged 3-8 months. Previous work has shown that for adult observers the illusory-contour strength increases proportionally with the support ratio. When the support ratio was relatively high (66%), infants preferred illusory contours to non-illusory figures by 3-4 months of age (experiment 1). In contrast, only infants 7-8 months old showed this preference for illusory contours when the support ratio was reduced to 37% (experiment 3). Further, infants showed no preference for an outline version of the illusory-contour figure, which produced no illusory contours (experiment 2). This result confirms that the infants' preference reflects their perception of illusory contours. Our results show that (i) illusory-contour perception emerges at around 3-4 months of age, but (ii) that this ability is very limited until around 7-8 months of age.

Analysis of Variance↗

PubMed2003

Do infant Japanese macaques ( Macaca fuscata) categorize objects without specific training?

In the present study, we examined whether infant Japanese macaques categorize objects without any training, using a similar technique also used with human infants (the paired-preference method). During the familiarization phase, subjects were presented twice with two pairs of different objects from one global-level category. During the test phase, they were presented twice with a pair consisting of a novel familiar-category object and a novel global-level category object. The subjects were tested with three global-level categories (animal, furniture, and vehicle). It was found that they showed significant novelty preferences as a whole, indicating that they processed similarities between familiarization objects and novel familiar-category objects. These results suggest that subjects responded distinctively to objects without training, indicating the possibility that infant macaques possess the capacity for categorization.

Analysis of Variance↗

PubMed2003

Infants' perception of illusory contours in static and moving figures.

We investigated 3-8-month-olds' (N=62) perception of illusory contours in a Kanizsa figure by using a preferential looking technique. Previous studies suggest that this ability develops around 8 months of age. However, we hypothesized that even 3-4-month-olds could perceive illusory contours in a moving figure. To check our hypothesis, we created an illusory contour figure in which the illusory square underwent lateral movement. By rotating the elements of this figure, we created non-illusory contour figures. We found that: (1) infants preferred moving illusory contours to non-illusory contours by 3-4 months of age, and (2) only 7-8-month-olds preferred static illusory contours. Our findings demonstrate that motion information promotes infants' perception of illusory contours. Our results parallel those reported in the study of partly occluded objects ().

Child Development↗