Capturing visual attention and the curve tracing operation.

The hypothesis that orienting visual attention is an important component of visual curve tracing was investigated. Ss examined a visual display and decided as quickly as possible whether 2 dots were on the same or different curves. The rate of tracing was determined by measuring the effects of curve distance on response time. Attention was directed to a curve by momentarily presenting it at a higher luminance. Directing attention to a curve that had 2 dots on it resulted in faster tracing rates with large benefits in overall response time. Directing attention to a distractor curve resulted in slower tracing rates and sizable costs in overall response times. Two alternative nonattentional explanations (eye movements and visible persistence) were examined and rejected. The role of attention in curve tracing is discussed in terms of the selective nature of curve tracing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response selection and response execution in task switching: Evidence from a go-signal paradigm.

The present study used a go/no-go signal delay (GSD) to explore the role of response-related processes in task switching. A go/no-go signal was presented at either 100 ms or 1,500 ms after the stimulus. Participants were encouraged to use the GSD for response selection and preparation. The data indicate that the opportunity to select and prepare a response (i.e., long GSD) resulted in a substantial reduction of task-shift costs (Experiment 1) and n-2 task-repetition costs (i.e., backward inhibition; Experiment 2) in the current trial. These results suggest that interference from the preceding trial can be resolved during response selection and preparation. Furthermore, the shift costs and the n-2 repetition costs after no-go trials with long GSD (i.e., response selection but no execution) were markedly smaller than after go trials. These findings suggest that the interference that gives rise to shift costs and n-2 repetition costs is related not solely to response selection but also to response execution. Thus, the present study demonstrates dissociable contributions of response selection and response execution to interference effects in task switching. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Apomorphine modifies the visual responses of cells in the rabbit's lateral geniculate nucleus

It has been shown that enhancing or reducing dopaminergic activity in the retina modifies the balance between center and surround responses of retinal neurons such as ganglion cells. We investigated how these changes are reflected in the dorsal lateral geniculate nucleus (dLGN) by studying the effects of injections of apomorphine, a mixed D1 and D2 agonist of dopamine, on the visual responses of geniculate cells. Experiments were carried out on anesthetized adult pigmented rabbits. A varnished tungsten microelectrode was used to record single-unit activity in the dLGN. The flash electroretinogram was also recorded to monitor retinal changes and to confirm the success of the injections. Apomorphine was injected intravitreally or intravenously. The results can be summarized as follows. Apomorphine decreased the amplitude of the b-wave of the electroretinogram. For most dLGN cells, apomorphine produced a strong reduction in response amplitude evoked by sine-wave grating stimuli, presented at various spatial frequencies. Responses to flashing spots were also reduced but to a much lesser extent than those to gratings. In addition, the balance between the responses to small and large spots changed in favor of large stimuli. Consequently, after injection of apomorphine, the geniculate cells were preferentially activated by large-sized flashing stimuli. These data suggest that apomorphine can reduce the spatial contrast sensitivity of cells in the dLGN. This effect could be mediated by the reduction of the strength of lateral inhibition at the retinal level.     

Rotated object identification with and without orientation cues.

The time to name two-dimensional line drawings of objects increases linearly for object rotations between 00 and 1200 from the upright. Several theories attribute these effects of orientation to finding the top or the top-bottom axis of objects. By this account, prior knowledge of the location of the top or the top-bottom axis of objects should diminish effects of object orientation when they are named. When this hypothesis was tested by cuing the top or the top-bottom axis, no reduction in the effects of orientation on object naming was found. This result is inconsistent with effects of orientation on object naming being due to finding the top or the top-bottom axis. Instead, the top may be found prior to rotational normalization of the object image. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Additivity and interaction between size ratio and response category in the comparison of size-discrepant shapes.

In Experiment 1, subjects made same–different judgments to pairs of shapes that could differ (irrelevantly) in size and in which different pairs combined distinct shapes. Size discrepancy had an effect both on same and different responses. It is argued that this nonmonotonicity was produced by a form of bias acting to slow different responses for same-sized pairs. Consistent with the proposed bias account, the nonmonotonic size-discrepancy effect on different trials was eliminated in Experiment 2, in which trials were blocked by size ratio. In Experiment 3, subjects performed a task similar to that in Experiments 1 and 2. However, additional visual information was added inside the bounding contour of the shapes, and this information was either the same or different across shapes. The match between within-contour information across shapes (whether same or different) was varied orthogonally with whether the bounding contours of the shapes were the same or different. In this experiment subjects decided whether the bounding contours of the shapes were the same or different, while ignoring the added information within the contours. When the added information matched across the two shapes, same responses were facilitated relative to when the added information mismatched. The converse occurred for different responses. This effect was more pronounced when the shapes were shown at the same size than when the shapes were at different sizes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus dimensionality effects in mental rotation

Do 3-dimensional (3-D) figures require more time to rotate mentally than do 2-dimensional (2-D) figures? This question was examined in 2 experiments incorporating 15 2-D and 15 3-D stimuli. For 3-D stimuli, block figures were used of the type used by R. N. Shepard and J. Metzler in their classic studies. For 2-D stimuli, block figures were also used, but with all cubes in a single plane, resulting in 2-D and 3-D figures matched on surface features. Three-D figures elicited steeper slopes than did 2-D figures, supporting the view that the mental rotation of visual representations is sensitive to stimulus dimensionality. The authors summarize the results of several mental rotation studies that investigated stimulus dimensionality and suggest that the evidence across studies is consistent with the present finding. They discuss 2 plausible loci for the dimensionality effect in S. M. Kosslyn's (1980) theory of mental imagery.     

The Time Course of the Contingent Spatial Blink.

Attentional capture is the unintentional deployment of attention to a task-irrelevant but attentionally salient object. The contingent involuntary orienting hypothesis states that it occurs only if a distractor's property matches current top-down attentional control settings (Folk, Remington, & Johnston, 1992). Folk, Leber, and Egeth (2002) found that monitoring a central RSVP stream for a coloured target led to spatial attentional capture by a peripheral distractor that matched the target colour. Using a similar paradigm, we explored the time course of this spatial blink. Implications of this study for current accounts of the attentional capture phenomenon are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A flow microcalorimetry investigation of the toxicity effects induced by aliphatic alcohols in a heterogeneous aerobic culture

An extensive investigation of the influence of aliphatic alcohols on the metabolic activity of a heterogeneous culture has been carried out using flow microcalorimetry as a monitoring technique. The response of the culture to the addition of alcohols (n-C₃ to n-C₈, t-C₄) has been examined for the microorganisms under endogenous conditions and substrate saturation conditions, and IC₅₀ values were determined for each state. For the n-alcohols, the inhibitory behavior was further examined through systematic variations of substrate and alcohol concentrations; the results yield inhibition patterns which show specific behavior both as function of alcohol concentration and alcohol chain length. Generally, the toxicity results obtained with the heterogeneous culture follow rather closely those found in homogeneous cultures. However, the initial effect of alcohols at low concentration show marked variations among various types of culture or when compared to other reference systems.     

Concurrent response-selection demands modulate the attentional blink.

The number of stimulus and response alternatives was varied in the 1st task of an attentional blink (AB) experiment (both tasks unspeeded) and in a speeded AB paradigm (SAB; speeded immediate response in Task?). Accuracy in Task? did not depend on the number of alternatives in the AB paradigm (Experiment 1); however, accuracy in Task? decreased as alternatives increased in the SAB paradigm (Experiments 2–3). Longer response times in Task? were associated with lower accuracy in Task?. The results suggest that the duration of central processing in Task? modulates the AB phenomenon. The results are discussed in the context of the central interference theory. The theory provides a unified theoretical framework within which the AB and SAB paradigms, the probe signal paradigm, and the psychological refractory period paradigm can be analyzed and understood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)