Responses to mirror-image stimulation in jungle crows (Corvus macrorhynchos)

Four jungle crows (Corvus macrorhynchos) were exposed to a mirror placed either vertically or horizontally. The most frequently observed behaviors were pecking at the mirror and wing flapping when looking toward the mirror. These behavior patterns, which were only rarely observed when the mirror was reversed, can be interpreted as aggressive behaviors against a conspecific. The vertical mirror evoked the behaviors more often than the horizontal mirror. The present results suggest that crows perceive their mirror image as an image of a conspecific, not as their own. Received: 16 December 1999 / Accepted after revision 29 January 2000     

Visual onset expands subjective time

We report a distortion of subjective time perception in which the duration of a first interval is perceived to be longer than the succeeding interval of the same duration. The amount of time expansion depends on the onset type defining the first interval. When a stimulus appears abruptly, its duration is perceived to be longer than when it appears following a stationary array. The difference in the processing time for the stimulus onset and motion onset, measured as reaction times, agrees with the difference in time expansion. Our results suggest that initial transient responses for a visual onset serve as a temporal marker for time estimation, and a systematic change in the processing time for onsets affects perceived time.     

Brain activation during the course of sentence comprehension

The purpose of this study is to determine, by functional magnetic resonance imaging, how the activated regions of the brain change as a Japanese sentence is presented in a grammatically correct order. In this study, we presented constituents of a sentence to Japanese participants one by one at regular intervals. The results showed that the left lingual gyrus was significantly activated at the beginning of the sentence, then the left inferior frontal gyrus and left supplementary motor area, in the middle of the sentence, and the left inferior temporal gyrus, at the end of the sentence. We suggest that these brain areas are involved in sentence comprehension in this temporal order.     

Left-side dominance for song discrimination in Bengalese finches (Lonchura striata var. domestica)

Male Bengalese finches are left-side dominant for the motor control of song in the sensorimotor nucleus (the high vocal center, or HVc) of the telencephalon. We examined whether perceptual discrimination of songs might also be lateralized in this species. Twelve male Bengalese finches were trained by operant conditioning to discriminate between a Bengalese finch song and a zebra finch song. Before training, the left HVc was lesioned in four birds and the right HVc was lesioned in four other birds. The remaining four birds were used as controls without surgery. Birds with a left HVc lesion required significantly more time to learn to discriminate between the two songs than did birds with a right HVc lesion or intact control birds. These results suggest that the left HVc is not only dominant for the motor control of song, but also for the perceptual discrimination of song. Accepted after revision: 11 September 2001 Electronic Publication     

The assumed effects of positive feedback paired with success on motivation to do a task: The cases of characters with high and low initial levels of interest

This study investigated the effects of positive feedback paired with success on motivation to do a task, and examined whether this differed according to whether the person performing the task had a high or low initial level of interest in that task. Subjects (448 junior college students) were asked to rate (from 0–10) the level of motivation of characters in four different stories. Subjects believed that positive feedback would encourage the character to do a task regardless of initial level of interest. However, when positive feedback could not be expected, ratings for motivation fell. Ratings for motivation were further analyzed when no positive feedback could be expected, either after an earlier experience of positive feedback paired with success or after success only (no feedback). In the case of a low initial level of interest, it was assumed that motivation would be increased after positive feedback, but in the case of a high initial level of interest motivation was assumed to be decreased by an earlier experience of positive feedback paired with success. These results suggest that the effect of positive feedback paired with success will differ according to the level of a person's initial interest.     

Effects of constrained choice on memory: The extension of the multiple-cue hypothesis to the self-choice effect

The self-choice effect is the phenomenon whereby self-chosen items are remembered better than experimenter-assigned items. This study examined whether the effect occurs when the choice is constrained by cuing, and whether the effect also occurs for unchosen items. In the experiment, 33 participants chose (choice condition) or were assigned (force condition) a target from three alternatives that were followed by a cue sentence as a criterion for the choice. Cue sentences corresponded to any of the three alternatives (free cuing) or to only one (constrained cuing). Participants then engaged in free recall of targets and subsequent recognition of all alternatives (chosen and unchosen items). Memory performance was enhanced by choice regardless of the constraints, but was also enhanced for unchosen items. These results indicate that "free choice" is not always critical for the self-choice effect, and that multiple cuing involving unchosen items is a plausible account for the retention advantage of choice procedures.     

Effect of spatial position on visual search for 3-D objects

We examined whether the position of objects in external space affects the visual-search task associated with the tilt of 3-D objects. An array of cube-like objects was stereoscopically displayed at a distance of 4.5 m on a large screen 1.5 m above or below eye height. Subjects were required to detect a downward-tilted target among upward-tilted distractors or an upward-tilted target among downward-tilted distractors. When the stimuli consisted of shaded parallelepipeds whose upper/bottom faces were lighter than their side faces, the upward-tilted target was detected faster. This result was in accordance with the 'top-view assumption' reported in previous research. Displaying stimuli in the upper position degraded overall performance. However, when the shaded objects whose upper/bottom faces were darker than their side faces were displayed, the detection of a downward-tilted target became as efficient as that of an upward-tilted target only at the upper position. These results indicate that it is possible for the spatial position of the stimulus to promote the detection of a downward-tilted target when shading and perspective information are consistent with the viewing direction.     

A reversed Ebbinghaus–Titchener illusion in bantams (Gallus gallus domesticus)

A disk surrounded by smaller disks looks larger, and one surrounded by larger disks looks smaller than reality. This visual illusion, called the Ebbinghaus–Titchener illusion, remains one of the strongest and most robust illusions induced by contrast with the surrounding stimuli in humans. In the present study, we asked whether bantams would perceive this illusion. We trained three bantams to classify six diameters of target disks surrounded by inducer disks of a constant diameter into “small” or “large”. In the test that followed, the diameters of the inducer disks were systematically changed. The results showed that the Ebbinghaus–Titchener figures also induce a strong illusion in bantams, but in the other direction, that is, bantams perceive a target disk surrounded by smaller disks to be smaller than it really is and vice versa. Possible confounding factors, such as the gap between target disk and inducer disks and the weighted sum of surface of these figural elements, could not account for the subjects’ biased responses. Taken together with the pigeon study by Nakamura et al. (J Exp Psychol Anim Behav Process 34:375–387 2008), these results show that bantams as well as pigeons perceive an illusion induced by assimilation effects, not by contrast ones, for the Ebbinghaus–Titchener types of illusory figures. Perhaps perceptual processes underlying such illusory perception (i.e., lack of contrast effects) shown in bantams and pigeons may be partly shared among other avian species.     

The number–time interaction depends on relative magnitude in the suprasecond range

Numerical representations influence temporal processing. Previous studies have consistently shown that larger numbers are perceived to last longer than smaller ones. However, whether this effect is modulated by the absolute or relative magnitudes of the numbers has yet to be fully understood. Here, participants observed single- and double-digit Arabic numerals in separate experimental blocks and reproduced stimulus duration of 600 or 1200 ms. Our results replicated previous findings that the duration of larger numbers was reproduced longer than that of smaller numbers within each digit set. Although the effect of numerical magnitude across single- and double-digit numerals was found when the numerals were presented for 600 ms, the difference was negligible when they were presented for 1200 ms, suggesting that relative magnitude is an important factor in the number–time interaction in the suprasecond range. These results suggest that contextual influence on number–time interaction may depend on the actual stimulus duration.