Evidence of separable spatial representations in a virtual navigation task

Three experiments investigated spatial orientation in a virtual navigation task. Subjects had to adjust a homing vector indicating their end position relative to the origin of the path. It was demonstrated that sparse visual flow was sufficient for accurate path integration. Moreover, subjects were found to prefer a distinct egocentric or allocentric reference frame to solve the task. "Turners" reacted as if they had taken on the new orientation during turns of the path by mentally rotating their sagittal axis (egocentric frame). "Nonturners," by contrast, tracked the new orientation without adopting it (allocentric frame). When instructed to use their nonpreferred reference frame, both groups displayed no decline in response accuracy relative to their preferred frame; even when presented with reaction formats based on either ego or allocentric coordinates, with format unpredictable on a trial, both groups responded highly accurately. These findings support the assumption of coexisting spatial representations during navigation.     

The development of organizational strategies in children: evidence from a microgenetic longitudinal study

The authors examined memory on a sort-recall task in children 8 to 12 years of age. Children were first classified as either strategic or nonstrategic on a sort-recall pretest and then participated in an 11-week microgenetic study involving nine sessions. Strategy use was assessed on each trial. Consistent with past longitudinal research, changes from nonstrategic to strategic behavior occurred suddenly rather than gradually. Once children began using organizational strategies, their recall performance improved immediately. Deliberate strategy use was clearly reflected by sorting behavior during encoding but not in clustering during recall. Conclusions about whether there are children with utilization deficiencies are thus affected by how the concept is defined and whether sorting or clustering is taken as the indicator of spontaneous strategy use.     

Visual search for dimensionally redundant pop-out targets: parallel-coactive processing of dimensions is location specific

Three visual search experiments investigated redundancy gains for single and dual odd-one-out feature targets that differed from distractors in orientation, color, or both. In Experiment 1, redundant-target displays contained (a) a single target defined in 2 dimensions, (b) dual targets each defined in a different dimension, or (c) dual targets both defined in the same dimension. The redundancy gains, relative to single nonredundant targets, decreased from the first condition on, with violations of J. Miller's (1982) race model inequality (RMI) manifested only in the first 2 conditions. Experiment 2 systematically varied the spatial separation between dual targets each defined in a different dimension. Violations of the RMI were evident only when the 2 targets occupied nearby locations. Experiment 3 provided evidence of RMI violations by dimensionally redundant targets at both precued (likely) and noncued (unlikely) display locations. Taken together, these results suggest that there is coactivation of a common mechanism by target signals in different dimensions (not by signals in the same dimension), that the coactivation effects are spatially specific, and that the coactivated mechanisms are located at a preattentive, perceptual stage of processing.     

Redundancy gains and costs in cognitive processing: effects of short stimulus onset asynchronies

In 7 experiments, the influence of varying stimulus onset asynchronies (SOAs) on the processing of redundant information about words and pseudowords was investigated. All stimuli were visually presented once or twice with 2 copies of the same item flashed either simultaneously or with short SOAs between presentations. The experiments revealed a redundancy gain for words that was absent for pseudowords. Furthermore, the redundancy gain disappeared at an SOA of 50 ms, and there was a gradual performance decline at longer SOAs. However, probing SOAs of 150 and 300 ms revealed that, compared with presentation of 1 target stimulus alone, words were processed significantly faster when target and redundantcopy appeared with a 150-ms lag. The results are tentatively explained in a neurocognitive framework.     

Can the spotlight of attention be shaped like a doughnut? Evidence from steady-state visual evoked potentials

Visual attention enables observers to extract and process high-priority information in the visual field. Controversy remains as to whether or not observers can ignore information that falls within the spatial beam of attention. We used an objective physiological measure, the steady-state visual evoked potential (SSVEP), to investigate this question. A stream of flickering small, uppercase letters was embedded in the center of a stream of large, uppercase letters. A unitary beam would result in no difference of the SSVEP amplitude elicited by the small letter stream when it was attended versus ignored (i.e., when subjects attended the large letter stream). Contrary to this prediction, SSVEP amplitude increased by almost 100% when the small letter stream was attended compared with when it was ignored. The results support the notion that the attentional spotlight can be formed like a doughnut, processing central information differentially depending on whether it is attended or ignored.     

Dimension-based visual attention modulates dual-judgment accuracy in Duncan's (1984) one- versus two-object report paradigm

Four experiments, adapting the object-judgment paradigm developed by J. Duncan (1984), examined the relationship between object-based and domain-based mechanisms of visual attention. The experiments demonstrated a cross-domain cost, in terms of accuracy, when observers made dual color-form judgments to one or two overlapping objects presented briefly, relative to within-domain, dual-color and dual-form judgments. This domain-based selection effect was additive to an object-based effect, a cost of making dual judgments to separate objects, as reported by J. Duncan (1984). The pattern of object- and domain-based effects points to a capacity limitation in how multidimensional features are bound into a coherent object representation, consistent with the dimension-weighting account of H. J. Miller, D. Heller, and J. Ziegler (1995), which postulates that there is a limit to the total selection weight available to be allocated to an object's dimensions.     

Probing distractor inhibition in visual search: inhibition of return

The role of inhibition of return (IOR) in serial visual search was reinvestigated using R. Klein's (1988) paradigm of a search task followed by a probe-detection task. Probes were presented at either the location of a potentially inhibited search distractor or an empty location. No evidence of IOR was obtained when the search objects were removed after the search-task response. But when the search objects remained on, a pattern of effects similar to Klein's results emerged. However, when just the search-critical object parts were removed or when participants received immediate error feedback to prevent rechecking of the search objects, IOR effects were observed only when probes appeared equally likely at search array and empty locations. These results support the operation of object-based IOR in serial visual search, with IOR demonstrable only when rechecking is prevented (facilitating task switching) and monitoring for probes is not biased toward search objects.     

Right amygdalar and temporofrontal activation during autobiographic, but not during fictitious memory retrieval

What distinguishes the recall of real-life experiences from that of self-created, fictitious emotionally laden information? Both kinds of information belong to the episodic memory system. Autobiographic memories constitute that part of the episodic memory system that is composed of significant life episodes, primarily of the distant past. Functional imaging was used to study the neural networks engaged in retrieving autobiographic and fictitious information of closely similar content. The principally activated brain regions overlapped considerably and constituted temporal and inferior prefrontal regions plus the cerebellum. Selective activations of the right amygdala and the right ventral prefrontal cortex (at the level of the uncinate fascicle interconnnecting prefrontal and temporopolar areas) were found when subtracting fictitious from autobiographic retrieval. Furthermore, distinct foci in the left temporal lobe were engaged. These data demonstrate that autobiographic memory retrieval uses (at least in non-brain damaged individuals) a network of right hemispheric ventral prefrontal and temporopolar regions and left hemispheric lateral temporal regions. It is concluded that it is the experiential character, its special emotional infiltration and its arousal which distinguishes memory of real-life from that of fictitious episodes. Consequently, our results point to the engagement of a bi-hemispheric network in which the right temporo-prefrontal hemisphere is likely to be responsible for the affective/arousal side of information retrieval and the left-hemispheric temporal gyrus for its engram-like representation. Portions of the neural activation found during retrieval might, however, reflect re-encoding processes as well.     

Investors versus Workers: A Class-Based Critique of International Investment Treaties

Bilateral investment treaties constitute an important instrument to facilitate global investment. Recent discussions in political theory have highlighted several normative concerns raised by bilateral investment treaties. One worry is that investment treaties undermine national self-determination as they grant investors far-reaching protections that can be legally enforced. Another worry is that the benefits and burdens entailed in bilateral investment treaties are distributed unfairly in a way that benefits investors at the expense of states and disadvantaged groups within states. Instead of critiquing bilateral investment treaties from a perspective of global (distributive) justice, in this article I develop a class-based critique. This involves a twofold departure. First, the article shifts the focus from distributions to the power relations that are built into the global capitalist economy and that come into sharp relief in the practice of global investment. Second, rather than focusing on the relation between states and investors, I claim that in a class-based critique the relation between workers and investors should take centre stage. I argue that bilateral investment treaties are effectively an instrument of class domination, insofar as they reproduce and increase the power of transnational corporations while at the same time decreasing the power of workers.