S. P. Vecera and M. J. Farah (1994) have addressed the issue of whether visual attention selects objects or locations. They obtained data that they interpreted as evidence for attentional selection of objects from an internal spatially invariant representation. A. F. Kramer, T. A. Weber, and S. E. Watson question this interpretation on both theoretical and empirical grounds. First, the authors suggest that there are other interpretations of the Vecera and Farah data that are consistent with location-mediated selection of objects. Second, they provide data, using the displays employed by Vecera and Farah in conjunction with a postdisplay probe technique, that suggests that attention is directed to the locations of the target objects. The implications of the results for space and object-based attentional selection are discussed.

The authors used a lexical-decision task in 3 different experiments to examine whether age differences in word recognition were consistent across processing stage. In all experiments, word frequency and length were manipulated. In Experiments 1 and 2, encoding difficulty was varied, and in Experiment 3, response selection difficulty was varied. In all 3 experiments, there were no age differences for word frequency. However, in Experiments 1 and 2, older adults showed a larger decrement for encoding. In Experiment 3, age differences were larger when response selection load increased. These results suggest that age differences in word recognition occur because older adults exhibit primarily peripheral-rather than central-processing decrements. The implications of these data for generalized and localized slowing models are discussed.

The authors report 4 lexical decision experiments in which case type, word frequency, and exposure duration were varied. These data indicated that there is a larger mixed-case disadvantage for nonwords than for words for longer duration presentations of targets. However, when targets were presented for 100 ms (followed by a postdisplay pattern mask), a larger mixed-case disadvantage occurred for words than for nonwords. For word frequency, the data from Experiments 1, 2, and 3 revealed a slightly larger mixed- case disadvantage for higher frequency words than for lower frequency words. (There was additivity between word frequency and case type for experiment 4.) These results are consistent with a holistically biased, hybrid model of visual word recognition but inconsistent with analytically biased, hybrid models of word recognition, such as the process model (Besner & Johnston, 1989) and the interactive-activation model (McClelland & Rumelhart, 1981).

In 2 experiments, younger and older adults were presented with simple multiplication problems (e.g., 4 x 7 = 28 and 5 x 3 = 10) for their timed, true or false judgments. All of the effects typically obtained in basic research on mental arithmetic were obtained, that is, reaction time (a) increased with the size of the problem, (b) was slowed for answers deviating only a small amount from the correct value, and (c) was slowed when related (e.g., 7 x 4 = 21) versus unrelated (e.g., 7 x 4 = 18) answers were presented. Older adults were slower in their judgments. Most important, age did not interact significantly with problem size or split size. The authors suggest that elderly adults' central processes, such as memory retrieval and decision making, did not demonstrate the typical age deficit because of the skilled nature of these processes in simple arithmetic.

Pioneer Hi-Bred International, Johnston, lowa 50130-0038The pl gene encodes a regulatory protein that controls the transcription of a number of structural genes of the anthocyanin biosynthetic pathway i n maize. pl alleles have been classified phenotypically into two categories: dominant (Pr) alleles lead to intense, light-independent pigmentation in vegetative and floral organs of the plant; recessive "sun-red" alleles (pr) lead to light-dependent red pigmentation in which only tissues exposed to light become pigmented. Based on these observations, two alternate pathways leading to anthocyanin synthesis in the plant have been proposed: one requiring light and the other bypassing the light requirement through the action of Pl. To evaluate this hypothesis, we have analyzed light-independent and light-dependent alleles of pl. Sequence analysis revealed that the two types of alleles have very distinct promoters but have the capacity to encode very similar proteins. The protein encoded by one recessive allele was shown to be functional in transient assays. Measurements of husk mRNA levels by quantitative polymerase chain reaction showed that sun-red pl alleles are expressed at much lower levels than a Pl allele, but their expression is increased approximately sixfold by exposure to light. These results lead to the conclusion that the sun-red pl alleles are not null; instead, they synthesize functional mRNA and protein. We propose that the light-dependent pigmentation observed in pl plants is the result of a threshold effect in which light exposure boosts pl mRNA expression past a crucial level necessary to generate sufficient PL protein molecules to activate transcription of the anthocyanin structural genes.