Eye movements were monitored during the performance of triple conjunction search tasks. Stimuli varied in color, shape, and orientation. Across trials, the target was either present or absent, and displays consisted of 6, 12, or 24 stimuli. Stimulus discriminability was manipulated for the shape dimension, with half of the participants seeing displays of Es and Fs (low-discriminability [LD] condition) and half seeing displays of Cs and Ts (high-discriminability [HD] condition). Participants in both conditions performed two search tasks. In the single-feature (SF) task, the target stimulus shared one feature with each of the distractors, whereas in the two-feature (TF) task, it shared two features with each distractor. An examination of saccadic endpoints revealed that participants were more likely to fixate on distractor stimuli sharing color (SF task) or color and shape (TF task) with the target. This was a robust finding, being observed across participants, saccades of different amplitudes and sequential position, and following short and long latencies to move. The extent to which participants made use of shape information increased with discriminability.

Localization of mechanotransduction in sensory hair cells to hair bundles requires selective targeting of essential proteins to specific locations. Isoform 2 of the plasma-membrane Ca 2ϩ -ATPase (PMCA2), required for hearing and balance, is found exclusively in hair bundles. We determined the contribution of splicing at the two major splicing sites (A and C) to hair-cell targeting of PMCA2. When PMCA2 isoforms were immunoprecipitated from purified hair bundles of rat utricle, 2w was the only site A variant detected; moreover, immunocytochemistry for 2w in rat vestibular and cochlear tissues indicated that this splice form was located solely in bundles. To demonstrate the necessity of the 2w sequence, we transfected hair cells with PMCA2 containing different variants at splice sites A and C. Although native hair bundles exclusively use the 2a form at splice-site C, epitope-tagged PMCA2w/a and PMCA2w/b were both concentrated in bundles, indicating that site C is not involved in bundle targeting. In contrast, PMCA2z/a was excluded from bundles and was instead targeted to the basolateral plasma membrane. Bundle-specific targeting of PMCA2w/a tagged with green fluorescent protein (GFP) was diminished, suggesting that GFP interfered with splice-site A. Together, these data demonstrate that PMCA2w/a is the hairbundle isoform of PMCA in rat hair cells and that 2w targets PMCA2 to bundles. The 2w sequence is thus the first targeting signal identified for a hair-bundle membrane protein; moreover, the striking distribution of inner-ear PMCA isoforms dictated by selective targeting suggests a critical functional role for segregated pathways of Ca 2ϩ transport.

The plasma membrane of vertebrate hair bundles interacts intimately with the bundle cytoskeleton to support mechanotransduction and homeostasis. To determine the membrane composition of bundles, we used lipid mass spectrometry with purified chick vestibular bundles. While the bundle glycerophospholipids and acyl chains resemble those of other endomembranes, bundle ceramide and sphingomyelin nearly exclusively contain short-chain, saturated acyl chains. Confocal imaging of isolated bullfrog vestibular hair cells shows that the bundle membrane segregates spatially into at least three large structural and functional domains. One membrane domain, including the stereocilia basal tapers and ~1 μm of the shaft, the location of the ankle links, is enriched in the lipid phosphatase PTPRQ (protein tyrosine phosphatase Q) and polysialylated gangliosides. The taper domain forms a sharp boundary with the shaft domain, which contains the plasma-membrane Ca2+-ATPase PMCA2 and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2); moreover, a tip domain has elevated levels of cholesterol, PMCA2, and PI(4,5)P2. Protein mass spectrometry shows that bundles from chick vestibular hair cells contain a complete set of proteins that transport, synthesize, and degrade PI(4,5)P2. The membrane domains have functional significance; radixin, essential for hair-bundle stability, is activated at the taper-shaft boundary in a PI(4,5)P2-dependent manner, allowing assembly of protein complexes at that site. Membrane domains within stereocilia thus define regions within hair bundles that allow compartmentalization of Ca2+ extrusion and assembly of protein complexes at discrete locations.

Eye movements were monitored while subjects performed parallel and serial search tasks. In Experiment la, subjects searched for an "O" among "X"s (parallel condition) and for a "T" among "L"s (serial condition). In the parallel condition of Experiment lb," T " was the target and "O"s were distractors; in the serial condition, these stimuli switched roles. Displays contained 1, 12, or 24 stimuli, with both target-present and target-absent trials. RT and eye-movement measures (number of fixations, saccadic error, and latency to move) indicated that search efficiency was greatest in the parallel conditions, followed by the serial condition of Experiment la and, finally, by the serial condition of Experiment lb. This suggests that eye movements are correlated with the attentional processes underlying visual search.

No abstract

In August-September 1996, personnel from Prewitt and Associates, Inc., conducted a cultural resources survey of ca. 725 acres of the former Leander Rehabilitation Center. The project area lies adjacent to U.S. Highway 183 and FM 620 in southern Williamson County, Texas. The survey resulted in additional documentation of one previously recorded prehistoric archeological site (41 WM452), the identification and recording of four historic archeological sites (41WM892, 41WM893, 41WM896, and 41WM897), and reconnaissance-level documentation of 45 historic buildings and structures. Site 41WM452 is an extensive upland lithic scatter and lithic procurement site which lacks subsurface deposits, features, and datable materials. Site 41WM892 is a wood-chopper camp that contains a number of rock alignments and limited artifact deposits dating to the first decade of the twentieth century. Site 41WM893 is a remnant of a railroad spur used during the 1937-1941 construction of Marshall Ford Dam (now Mansfield Dam). Site 41WM896 contains a small number of features and sparse artifact deposits associated with the 1937-1945 Rhodes farmstead. Site 41WM897 is an isolated historic well with unknown associations. None of these archeological sites contains important information, and it is recommended that they be considered not eligible for listing in the National Register of Historic Places or for designation as State Archeological Landmarks. The 45 buildings and structures, at 36 locations, are associated with the former State Dairy and Hog Farm. This farm was established in 1942, expanded after 1945, and reached its peak years of production as a hog farm between 1950 and the late 1960s, Created to serve the needs of the State Board of Control and the State Hospital, the facility is significant for its success in food production for eleemosynary institutions in Austin and throughout Texas, as well as for its role in the application of modern psychiatric treatment based on the therapeutic value of manual labor. Among the surveyed resources are dwellings, an office and warehouse building, a dormitory, a variety of agricultural buildings and structures, and infrastructural elements, all built between 1943 and 1955. Twenty-one of the 45 surveyed resources are recommended as being eligible for listing in the National Register of Historic Places under Criteria A and C as Contributing resources in a historic district and for designation as State Archeological Landmarks.