Akihiro Izumi

Auditory stream segregation in Japanese monkeys

Japanese monkeys were examined to determine whether they perceptually segregate tone sequences. Monkeys were required to discriminate two sequences of tones (target sequences) differing in frequency contours. Distractor sequences were presented simultaneously with the target sequences. Monkeys could discriminate the sequences when the frequency ranges of the target and distractor sequences did not overlap, but they could not when the ranges overlapped. Subsequent probe tests confirmed that the discrimination depended on cues other than the local pitch of the component tones regardless of the presence of the distractor sequence. The results suggest that monkeys segregate tone sequences based on frequency proximity, and they perceive global characters of the segregated streams.

Japanese monkeys perceive sensory consonance of chords

Consonance/dissonance affects human perception of chords from early stages of development [e.g., Schellenberg and Trainor, J. Acoust. Soc. Am. 100, 3321-3328 (1996)]. To examine whether consonance has some role in audition of nonhumans, three Japanese monkeys (Macaca fuscata) were trained to discriminate simultaneous two-tone complexes (chords). The task was serial discrimination (AX procedure) with repetitive presentation of background stimuli. Each tone in a chord was comprised of six harmonics, and chords with complex ratios of fundamental frequency (e.g., frequency ratio of 8:15 in major seventh) resulted in dissonance. The chords were transposed for each presentation to make monkeys attend to cues other than the absolute frequency of a component tone. Monkeys were initially trained to detect changes from consonant (octave) to dissonant (major seventh). Following the successful acquisition of the task, transfer tests with novel chords were conducted. In these transfer tests, the performances with detecting changes from consonant to dissonant chords (perfect fifth to major seventh; perfect fourth to major seventh) were better than those with detecting reverse changes. These results suggested that the consonance of chords affected the performances of monkeys.

Development of a compact and general-purpose experimental apparatus with a touch-sensitive screen for use in evaluating cognitive functions in common marmosets

Common marmosets have been used extensively in biomedical research and the recent advent of techniques to generate transgenic marmosets has accelerated the use of this model. New methods that efficiently assess the degree of cognitive function in common marmosets are needed in order to establish their suitability as non-human primate models of higher brain function disorders. Here, we have developed a new apparatus suitable for testing the cognitive functions of common marmosets. Utilizing a mini laptop PC with a touch-sensitive screen as the main component, the apparatus is small and lightweight and can be easily attached to the home cages. The ease of designing and testing new paradigms with the flexible software is another advantage of this system. We have tested visual discrimination and its reversal tasks using this apparatus and confirmed its efficacy.

Object discrimination learning in aged Japanese monkeys.

The authors investigated the behavioral aging effects of Japanese macaques in 3 object discrimination learning tasks: learning-set (LS) formation, go/no-go discrimination learning, and multiple discrimination reversals. Aged monkeys showed deteriorated performance in these tasks compared with younger controls. Hypothesis analysis of LS showed that aged monkeys had difficulty learning the lose-shift component of the hypothesis win-stay-lose-shift with respect to object. Deficits in go/no-go successive discrimination were clear in no-go trials only in the first 2 pairs of 5 tasks. Performance of aged monkeys was severely disturbed from a chance to criterion level in discrimination reversals. These results are attributed not only to increased tendency for perseveration but also to difficulty in associating the reward and the object in aged monkeys and may be related to the decline in the functions of the ventral frontal cortex.

Relative pitch perception in Japanese monkeys (Macaca fuscata).

To investigate whether monkeys perceive relative pitch, the author trained 3 Japanese monkeys (Macaca fuscata) to detect changes from rising to falling contours of 3-tone sequences. Tone sequences were presented serially with transposition, so monkeys were urged to attend to cues other than the absolute frequency of a component tone. Results from probe tests with novel sequences showed that monkeys discriminated by the relative pitch when the frequency ranges of sequences were within the training range, showing a similar tendency as birds in previous studies (e.g., S. H. Hulse, J. Cynx, & J. Humpal, 1984).

Time course of vocal modulation during isolation in common marmosets (Callithrix jacchus).

Common marmosets vocalize phee calls as isolation calls, which seem to facilitate their reunion with family groups. To identify multiple acoustic properties with different time courses, we examined acoustic modulations of phees during different social contexts of isolation. Subject marmosets were totally isolated in one condition, were visually isolated and could exchange vocalizations in another condition, and were visually isolated and subsequently totally isolated in a third condition. We recorded 6,035 phees of 10 male–female marmoset pairs and conducted acoustic analysis. The marmosets frequently vocalized phees that were temporally elongated and louder during isolation, with varying time courses of these changes in acoustic parameters. The vocal rates and sound levels of the phees increased as soon as the marmosets saw their pair mates being taken away, and then gradually calmed down. The phee duration was longer in conditions during which there were no vocal responses from their pair mates. Louder vocalizations are conspicuous and seem to be effective for long‐distance transmission, whereas shorter call duration during vocal exchanges might avoid possible vocal overlap between mates. Am. J. Primatol. 72:681–688, 2010.

Effect of temporal separation on tone-sequence discrimination in monkeys

Perception of auditory spectral-temporal patterns was examined in two Japanese monkeys. The stimuli used were pairs of pure tones of different frequencies that were presented sequentially. The monkeys were required to discriminate whether the frequency of the second tone was higher or lower than the first tone. The performances of the monkeys deteriorated when a temporal gap (i.e., silence) was inserted between the component tones. A comparison experiment did not show such effects in human participants. The results suggested that monkeys use frequency transitions for tone-sequence discrimination, and that local characters are more dominant discrimination cues in monkeys than in humans.

Temporal rules in vocal exchanges of phees and trills in common marmosets (Callithrix jacchus)

Marmosets exchange two types of calls: phees and trills. We played back phees and trills to investigate the temporal rules of vocal exchanges using ten captive common marmosets (Callithrix jacchus). The marmosets usually emitted the same type of vocalizations just after the stimulus playbacks, and similar regularities were observed in the temporal intervals of phees and in trills. They vocalized with shorter intervals when they responded with trills rather than phees, and, after the first call, they repeatedly vocalized trills with shorter intervals than phees. These results suggest that the temporal rules between phees and trills are qualitatively similar but quantitatively different. These results might be owing to the different distances over which these contact calls are used. Am. J. Primatol. 71:617–622, 2009.

Food transfer in common marmosets: parents change their tolerance depending on the age of offspring

Food transfer is considered to provide infants with additional nutrients during weaning, and in fact, its frequency peaks around this time. However, the mechanisms underlying such food transfer remain unclear. In this study, we investigated whether adult common marmosets (Callithrix jacchus) change their tolerance to offspring begging for food depending on the offsprings age. We used four families consisting of breeding pairs, older offspring (29–49 weeks old), and younger offspring (7–15 weeks old). To directly compare the responses of a parent with its older and younger offspring, we placed one parent and one offspring in a testing space at one time. We presented foods where only the parent could reach them to ensure that the foods were transferred from the parent to offspring. Younger offspring showed more interest in food being held by the parents than older offspring. Parents refused older offspring more frequently than younger offspring and transferred food more often to younger offspring than to older offspring. There was no difference in all behavioral categories between fathers and mothers. These results suggest that both fathers and mothers are more tolerant to weanlings, but their tolerance decreases as offspring mature. Am. J. Primatol. 70:999–1002, 2008.

The Effect of Marker Frequency Disparity on the Discrimination of Gap Duration in Monkeys

Duration-discrimination thresholds of the silent interval (gap) between two successive tones (markers) were measured in four Japanese monkeys. The task was serial discrimination, and monkeys were required to release the lever when the gap duration decreased from 200 ms. Monkeys successfully acquired the task, and gap thresholds of monkeys were revealed to be larger than previous data with human subjects. Gap thresholds were not affected by marker frequency when the two markers were identical in frequency, though the thresholds increased when large frequency differences existed between markers. The effect of marker frequency disparity on gap thresholds in monkeys is discussed in terms of the difficulty in integrating information from discrete frequency channels.