Considering that the nature of the input is one of the most important variables in determining how the brain will process information, findings from tachistoscopic studies aimed at assessing hemispheric specializations are examined in terms of the characteristics of the incoming information either available or required for processing. The basic features of the tachistoscopic technique are analyzed, and a framework for further investigation is suggested along with a reinterpretation of existing evidence. In a subsequent series of four experiments, several assumptions and interpretations made earlier are empirically tested. In a second series of three experiments, hemispheric asymmetries are examined with respect to the properties of the visual system and its capacity to extract information in terms of the spatial-frequency spectral components of a stimulus. Methodological and theoretical implications of the results are discussed, and an account of cerebral specialization suggesting a hemispheric sensitivity to different aspects of the same information is proposed.

This thesis explores the visual functions of the right anterior temporal cortex of the human brain. In Part 1, 92 patients with unilateral temporal- or frontal-lobe excisions and 35 normal control subjects were tested under two experimental conditions (global, local) of a reaction-time task, employing hierarchically structured letters or designs as stimuli. In both versions, the right temporal-lobe group was less affected than other groups by interference from the global aspect of the stimulus. These findings support the hypothesis that the right temporal lobe contributes to global visual processing. In Part 2, the ability to learn a cue-system for discriminating between two targets against a background of visually similar items was examined in 107 patients with unilateral temporal- or frontal-lobe excisions and 37 control subjects, using three versions of a visual-cue learning task. With letters and nonsense syllables, all groups took longer to complete the task when the background information was changed after three learning trials. With abstract designs, only patients with right temporal-lobe lesions failed to show this interference effect after three learning trials, but did so after six. Hence, it is argued that the right temporal lobe plays a role in visual pattern-discrimination learning.

The work reported here was aimed at extending previous findings suggesting that the medial and lateral substantia nigra (SN) are functionally different with regard to intracranial self-stimulation (ICSS) and circling. It was found that the effects of systemic D- and L-amphetamine on ICSS were different for medial and lateral SN sites. These differences were attributed to the presence of two subtypes of dopamine (DA) neurons in the SN. The circling results indicate that circling in opposite directions can be elicited from the medial and lateral parts of the nigrostriatal DA system from the same hemisphere suggesting that medial and lateral nigrostriatal DA have opposing roles in the expression of circling. It was further demonstrated that the superior colliculus is critical for the expression of medial SN derived circling and the midbrain reticular formation is critical for both medial and lateral SN derived circling.

This study examined the contributions of different brain areas to several of the behavior effects of amphetamine. The drug was micro-injected into each of six discreet brain sites in rats and the effects on behavior were examined. Amphetamine's rewarding effects were studied using the conditioned place preference (CPP) paradigm. Animals that had received injections into the nucleus accumbens showed a CPP, suggesting a rewarding effect of the drug. No effect was produced by injections into the medial frontal cortex, medial or lateral parts of the caudate nucleus, amygdala or the region around the area postrema. A conditioned taste aversion (CTA) towards a flavour that had been paired with the drug was produced by injections into the region around the area postrema, but not from the other sites. Anorexia and adipsia were both producted only by injections into the nucleus accumbens and amygdala. In the open field, increased activity was produced by intra-accumbens amphetamine injections, with smaller effects from the medial frontal cortex and medial caudate. Stereotyped behavior was not produced by any intra-cranial injection. The CPP, anorexia, adipsia and increase in activity that were produced by the intra-accumbens injections were interpreted as suggesting that the drug had stimulated approach behavior towards all stimuli, as if they had all become rewarding. The observation of a CPP from the accumbens and a CTA from the region around the area postrema suggests that the rewarding and apparently aversive effects of systemically injected amphetamine result from actions of the drug on different neuroanatomical substrates. Other hypotheses of the behavioral function of the neural substrates of the observed effects are presented.

A name identity task was used to assess the language processing abilities of the right hemisphere of the brain. Ten undergraduates participated in each of three experimental conditions; nouns presented below threshold, nouns presented above threshold and verbs presented above threshold. Significant priming effects occurred when a picture of a noun or verb was presented above threshold and followed by a word which named the picture. The priming effect for nouns presented below threshold was not significant. No hemispheric asymmetries were found for the recognition of nouns or verbs.

In Part I, recall of spatial location was studied in an incidental-learning situation, where patients with unilateral brain lesions, the amnesic patient, H. M., and normal control subjects were asked to estimate the prices of objects in an array. All patient groups could encode location normally, but patients with right temporal-lobe lesions that included extensive hippocampal removal showed abnormally rapid forgetting. For all groups, and for H. M., location-recall did not differ under automatic and under effortful encoding conditions. It is argued that these results point to the importance of hippocampal-ceocortical interactions in spatial memory. In Part II, patients with frontal-lobe lesions were shown to be impaired in judging the frequency with which words or designs occurred in a list. With words, the deficits were demonstrable for both examiner-provided and self-generated stimuli. This impairment may be attributable either to a disorderly search process or to a deficit in cognitive estimation, or both.

Thesis (Ph.D.)--Biomedical Engineering, Georgia Institute of Technology, 2007. / Committee Chair: Hu, Xiaoping; Committee Member: Brummer, Marijn; Committee Member: Butera, Robert; Committee Member: Oshinski, John; Committee Member: Sathian, Krish.

The P300 component of the average evoked potential was recorded at Pz during two divided visual field tasks. During a lexical decision task, reaction time and P300 latency were faster to stimuli in the right visual field, indicating that the latency of the P300 may be a useful measure in laterality research. A right visual field advantage was obtained for reaction time in a face perception task and the P300 latency difference showed a similar but non-significant advantage. Use of the P300 latency to assess the validity of the assumptions underlying the application of an additive factors model to divided visual field studies of cerebral assymetry was discussed. The present evidence suggests that the assumptions are valid. / Arts, Faculty of / Psychology, Department of / Graduate

An extensive mapping of the caudate-putamen in the rat for intracranial self-stimulation (ICS) sites »as undertaken to provide additional support for the role of dopamine in brain stimulation reward. Eighty-seven percent of the placements in the neostriatum supported ICS, with self-stimulation rates greater than 250/15 min at 56% of the sites. In a second experiment, animals were prepared with electrodes aimed at the lateral caudate-putamen. Those subjects displaying ICS subsequently received 6-hydroxydopamine lesions to the dopamine cell bodies in the substantia nigra pars compacta either ipsilateral or contralateral to the electrode. The destruction of the dopamine cell bodies attenuated ICS in both groups during the first post-lesion test sessions. However, the rates in the ipsilateral group declined to between 2-9% of control scores, whereas the rates in the contralateral group improved over testing to 72% of control values, 28 days after the lesion. On the basis of these data, it was concluded that unilateral destruction of the dopaminergic nigro-neostriatal (NSB) has two effects on ICS behaviour. First, unilateral reduction of neostriatal dopamine is accompanied by a loss of brain stimulation reward at sites normally innervated by the NSB, specifically the caudate-putamen. Secondly, lesions of the NSB produce a general disruption in bar pressing behaviour, as evidenced by the attenuation of ICS following contralateral lesions. The possible role of the NSB in natural reward is discussed. / Arts, Faculty of / Psychology, Department of / Graduate

The thesis describes research investigating differences between the two hemispheres in automatic and in attentionally controlled processes. It is suggested that the interaction between these two processes may be a source of hemispheric differences. Three different paradigms that each imply different definitions of automatic and attentionally controlled processes are used: A paradigm used to demonstrate illusory conjunctions, a modified priming paradigm and a modified Stroop-task. Converging evidence from all three paradigms indicates that automatic processes are common to both hemispheres. Lateral asymmetries only emerge in attentional effects. For verbal information, selective attention mechanisms in the left hemisphere are found to be selective for left hemisphere items only, whereas right hemisphere mechanisms are sensitive to information from both hemispheres. The right hemisphere appears to be able to give some automatic support to attended verbal processing in the left hemisphere, while the reverse seems to be more difficult. / Arts, Faculty of / Psychology, Department of / Graduate