Extra-dimensional shift

Fig. 1. Discriminative stimuli used in tests of intra- and extra-dimensional shifts of attention in marmosets with lesions of the prefrontal cortex (PFC) or 6-OHDA-induced depletion of DA from PFC. Plus and minus signs indicate reinforced and non-reinforced discriminanda, respectively. The arrows indicate those stages especially sensitive to PFC DA depletion as shown by Crofts et al. (2001). Adapted from Crofts et al. (2001).

Additional studies of striatal DA loss in the marmoset also show that this fails to impair extra-dimensional shift performance as affected by prefrontal cortical lesions (Collins et al., 2000). However, the striatal DA loss does produce an impairment in shifting between stimulus dimensions when the requirement is to shift back towards a previously irrelevant dimension, which is possibly relevant to impaired performance of human patients with Parkinson s disease of shifting between two well-established task sets (Cools et al., 2001). 

Downes JJ, Roberts AC, Sahakian BJ, Evenden JL, Robbins TW (1989) Impaired extra-dimensional shift performance in medicated and unmedicated Parkinson s disease Evidence for a specific attentional dysfunction. Neuropsychologia 27 1329-1344. 

Owen AM, Roberts AC, Hodges JR, Summers BA, Polkey CE, Robbins TW. Extra-dimensional versus intra-dimensional set shifting performance following frontal-lobe excisions, temporal-lobe excisions or amygdalo-hippocampectomy in man. Neuropsychologica 1991 29 993-1006. 

Consider now the total possible number of dispositions of the unit meshes of the structures of Fig. 14, including extra placements arising from the presence of steps on the surface [Eq. (9)]. Comparing fee (HI) and hep (1000) substrates, we note that the two-dimensional rotational symmetry of both is three-fold. However, in the 2-direction normal to these surfaces the packing of the fee surface is ABCABC. . . while that of the hep surface is ABABAB.. . . Because successive planes are shifted parallel to the surface, there are more possible dispositions of adsorbed structures upon the former than upon the latter if account is made of steps. Some of these possibilities are compared and summarized in Table III. For example, a simple (2x1) structure on fee (111) can have 18 distinct dispositions when adatoms are placed in three-fold sites. [If adatoms are instead bridged between two nearest neighbors of the... 

Dislocation in a two-dimensional crystal. The extra plane of atoms AB causes strain at bond CD. On breaking, the bond flips across to form CB. This incremental movement shifts the dislocation across so that the overall effect is to slide the two planes BDG and CF over each other. 

The A1 mas NMR studies were performed on heulandite-clinoptilohte series [00M3, OlSl, 02M1, 02X1, 08R1, lOGl]. These studies provide information about the environment of A1 atoms in the structure. " Al, in the three-dimensional framework, exhibits a chemical shift of <5 = 60 ppm If the extra-framework A1 occurs, this is characterized by a peak <) = 0 ppm. The appearance of peaks between 30...50 ppm can be coimected with the 5-coordinated A1 atoms or distorted tetrahedrally coordinated ones [99S4, OOTl]. 

For the acene and phene series, the UV-vis and fluorescence spectra shift dramatically when the number of the phenyl rings increases. In contrast, the shifts for all-benzenoid PAHs with either armchair or cove -type edges are small and they show a high chemical stability. Very recently, graphitic molecules with partial zig-zag periphery such as 68a, 68b and 73 (Scheme 3.19) were synthesized. It was found that the introduction of two or six extra re-centers onto the all-benzenoid graphitic molecules dramatically influences their electronic properties, chemical reactivity and two- and three-dimensional self-assembly [64]. 

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