In a previous study we investigated the effects of callosal transected lesions made 10 weeks earlier (the 10-week-old callosal transected lesions), either at 3 weeks of age or at 13 weeks of age, upon the acquisition of a black-white (BW) discrimination in rats either with one eye removed at birth (OEB) or at 13 weeks of age (OET) following lesions of the contralateral (CT) visual cortex to the remaining eye. The CT visual cortex lesions were performed right before the training of BW discrimination. We found that the 10-week-old callosal transected lesions facilitated the acquisition in OEBs when the callosal lesions were given at 3 weeks of age, and to a lesser extent at 13 weeks of age. We also found that the same type of callosal transected lesions did not do so in OETs, regardless of the age when the callosal lesions were made. Since the CT visual cortex lesions inevitably result in damage of the callosal neurons, and lead to de-generation of the callosal afferents in the ipsilateral (IP) visual cortex, the present study was undertaken to investigate if the CT visual cortex lesions made 10 weeks earlier (the 10-week-old CT visual cortex lesions), made either at 3 weeks of age or 13 weeks of age, would affect the acquisition of BW discrimination in OEBs and OETs, like the 10-week-old callosal transected lesions employed in the previous study mentioned above. We found that in both OEBs and OETs the overall pattern of the facilitation effects of the 10-week-old CT visual cortex lesions on the acquisition of BW discrimination is, in general, the same as that observed in the 10-week-old callosal transected lesions, but the facilitative effect of the 10-week-old CT visual cortex lesions is more prevailing and pronounced. The findings are discussed in relation to the possible involvement of neurotrophic factors, released when the CT visual cortex lesions were made, in synaptic reorganization, and also in relation to the possibility of the increased use of the uncrossed visual pathways.
The initial perceptual processing of native and foreign language characters was studied in ten Japanese, eight Chinese, and eight Korean subjects using ERPs to Chinese (Kanji) characters and Hangul. The stimuli were presented in AAAAABAA form (habituation paradigm), and the repetition stimulus A and test stimulus B were graphically similar, dissimilar, or identical. The ERP results showed that the P2 amplitude, which reduced to the repeated stimuli, recovered to test stimuli of the native language characters irrespective of similarity. There was no amplitude difference between similar and dissimilar test stimuli. For the foreign language characters, the degree of the P2 recovery was larger for dissimilar than similar and identical test stimuli. These findings indicated a mechanism that quickly detects even slight changes of visual patterns when they are well-learned native language characters, thereby orienting attention for further processing. The difference of detection rapidity was discussed in terms of holistic versus part-based perception.
The effects of attention on P300 from the auditory three-stimulus oddball tasks were examined. Twelve undergraduate students participated in three tasks. They were required to press a button to respond to the tar-get stimuli in an active task, while in an ignore task, they engaged themselves in another visual task. In a passive task, the subjects were given no special instructions about the stimulus sequences. Target (p =.15), standard (p =.70), and infrequent nontarget (p =.15) stimuli in a 'novels' condition were 2000 Hz tone, 1000 Hz tone, and 36 different novel sounds, and in a 'tones' condition, a novel sound, another novel sound, and 36 different tones which differed in frequency ranging from 523 to 3951 Hz, respectively. In the active task, target stimuli elicited P3b in both conditions. In addition, rare nontarget novel sounds elicited novelty P300 ('novels' condition), although rare nontarget tones elicited P3b ( 'tones' condition). In contrast, in the ignore and passive tasks, small P300 emerged only for the novel sounds in the 'novels' condition. The results suggest that when subjects do not pay attention to the stimulus sequences, the 'novel' characteristic of the rare stimuli in tone sequence are necessary for those stimuli to capture subject's attention.