Masahiro Shibasaki

Premenstrual enhancement of snake detection in visual search in healthy women

It is well known that adult humans detect images of snakes as targets more quickly than images of flowers as targets whether the images are in color or gray-scale. When such visual searches were performed by a total of 60 adult premenopausal healthy women in the present study to examine whether their performance would fluctuate across the phases of the menstrual cycle, snake detection was found to become temporarily enhanced during the luteal phase as compared to early or late follicular phases. This is the first demonstration of the existence of within-individual variation of the activity of the fear module, as a predictable change in cognitive strength, which appears likely to be due to the hormonal changes that occur in the menstrual cycle of healthy women.

The color red distorts time perception for men, but not for women

We investigated the effect of the color red on time perception using a temporal bisection task with human adults. The results showed that the perceived duration of a red screen was longer than was that of a blue screen. However, the results reflected sex differences; men, but not women, overestimated the duration of the red screen. Additionally, the reaction times to a red screen were faster than those to a blue screen, and we found a significant correlation between reaction time and the tendency to overestimate the duration of a red screen. Participants who reacted quickly to a red screen overestimated its duration. These results are discussed within the context of recent studies indicating that the color red exerts certain special psychological effects on human behavior.

Viewing images of snakes accelerates making judgements of their colour in humans: red snake effect as an instance of ‘emotional Stroop facilitation’

One of the most prevalent current psychobiological notions about human behaviour and emotion suggests that prioritization of threatening stimuli processing induces deleterious effects on task performance. In order to confirm its relevancy, 108 adults and 25 children were required to name the colour of images of snakes and flowers, using the pictorial emotional Stroop paradigm. When reaction time to answer the colour of each stimulus was measured, its value was found to decrease when snake images were presented when compared with when flower images were presented. Thus, contrary to the expectation from previous emotional Stroop paradigm research, emotions evoked by viewing images of snakes as a biologically relevant threatening stimulus were found to be likely to exert a facilitating rather than interfering effect on making judgements of their colour.

Japanese monkeys (Macaca fuscata) spontaneously associate alarm calls with snakes appearing in the left visual field.

Many socially living animals are sensitive to a potential predator as part of their antipredator strategy. Alarm calls function to deter predators and to help other group members detect danger. The left visual field is involved in detection of potential threats or predators in many vertebrates, but it is unclear how alarm calls influence visual detection of a potential predator. Here, we experimentally examined how alarm calls spontaneously influence the search for pictures of a potential predator in captive Japanese macaques. We used an audiovisual preferential-looking paradigm by presenting pictures of a snake and a flower simultaneous with either a recording of alarm calls or contact calls. We found no difference in gaze duration between the 2 picture types when playing back contact calls. Monkeys looked significantly longer at pictures of snakes than at those of flowers when alarm calls were played back if the snake pictures were presented on the left side of the monkeys visual field, indicating right hemispheric bias during processing of predator representations. This is the first laboratory demonstration of auditory enhancement of visual detection of predators in the left visual field in animals, which will contribute to a better understanding of alarm call studies conducted in the wild.

The Effect of Inversion on the Anger Superiority Effect in Children with andwithout Autism Spectrum Disorders

Previous studies have demonstrated that angry faces capture humans’ attention more rapidly than emotionally positive faces. This phenomenon is referred to as the anger superiority effect (ASE). Despite atypical emotional processing, adults and children with Autism Spectrum Disorders (ASD) have been reported to show ASE as well as typically developed (TD) individuals. In this study, we tested ASE in children with and without ASD using upright/ inverted schematic faces to explore the face-processing style employed by them during detection of emotional faces. The results revealed that faster detection of angry faces over happy faces was observed in both TD and ASD children. Interestingly, however, the effect was stronger in children with ASD compared to TD children when faces were inverted. These findings suggest that different face-processing style would be employed or different mechanisms of emotional processing would underlie the quick detection of angry faces in children with and without ASD.

Measurement of neuronal activity in a macaque monkey in response to animate images using near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) has been used extensively for functional neuroimaging over the past decade, in part because it is considered a powerful tool for investigating brain function in human infants and young children, for whom other neuroimaging techniques are not suitable. In particular, several studies have measured hemodynamic responses in the occipital region in infants upon exposure to visual stimuli. In the present study, we used a multi-channel NIRS to measure neuronal activity in a macaque monkey who was trained to watch videos showing various circus animals performing acrobatic activities without fixing the head position of the monkey. Cortical activity from the occipital region was measured first by placing a probe comprising a 3 × 5 array of emitters and detectors (2 × 4 cm) on the area (area 17), and the robustness and stability of the results were confirmed across sessions. Cortical responses were then measured from the dorsofrontal region. The oxygenated hemoglobin signals increased in area 9 and decreased in area 8b in response to viewing the videos. The results suggest that these regions are involved in cognitive processing of visually presented stimuli. The monkey showed positive responsiveness to the stimuli from the affective standpoint, but its attentional response to them was an inhibitory one.

Delayed disengagement of attention from snakes in children with autism.

In the visual search task, it is well known that detection of a tilted straight line as the target among vertical lines that act as distractors is easier than vice versa, and that detection of a snake image as the target among flower images is easier than vice versa. In this study, the degree of such search asymmetry was compared between 18 children with autism and 14 typically developing (TD) children. The results revealed that compared to TD children, children with autism were disproportionally slow when asked to detect the flower among the snake images, suggesting the possibility that they experienced difficulty of disengaging their attention from the snake images. This delayed disengagement would serve itself as an enhanced attentional bias toward snakes in children with autism that is similar to characteristics of visual search performance in anxiety patients.

Orthographic Reading Deficits in Dyslexic Japanese Children: Examining the Transposed-Letter Effect in the Color-Word Stroop Paradigm

In orthographic reading, the transposed-letter effect (TLE) is the perception of a transposed-letter position word such as “cholocate” as the correct word “chocolate.” Although previous studies on dyslexic children using alphabetic languages have reported such orthographic reading deficits, the extent of orthographic reading impairment in dyslexic Japanese children has remained unknown. This study examined the TLE in dyslexic Japanese children using the color-word Stroop paradigm comprising congruent and incongruent Japanese hiragana words with correct and transposed-letter positions. We found that typically developed children exhibited Stroop effects in Japanese hiragana words with both correct and transposed-letter positions, thus indicating the presence of TLE. In contrast, dyslexic children indicated Stroop effects in correct letter positions in Japanese words but not in transposed, which indicated an absence of the TLE. These results suggest that dyslexic Japanese children, similar to dyslexic children using alphabetic languages, may also have a problem with orthographic reading.