Fluid Intelligence Is (Much) More than Working Memory Capacity: An Experimental Analysis.

Empirical evidence suggests a great positive association between measures of fluid intelligence and working memory capacity, which implied to some researchers that fluid intelligence is little more than working memory. Because this conclusion is mostly based on correlation analysis, a causal relationship between fluid intelligence and working memory has not yet been established. The aim of the present study was therefore to provide an experimental analysis of this relationship. In a first study, 60 participants worked on items of the Advanced Progressive Matrices (APM) while simultaneously engaging in one of four secondary tasks to load specific components of the working memory system. There was a diminishing effect of loading the central executive on the APM performance, which could explain 15% of the variance in the APM score. In a second study, we used the same experimental manipulations but replaced the dependent variable with complex working memory span tasks from three different domains. There was also a diminishing effect of the experimental manipulation on span task performance, which could now explain 40% of the variance. These findings suggest a causal effect of working memory functioning on fluid intelligence test performance, but they also imply that factors other than working memory functioning must contribute to fluid intelligence.

Age-related differences in the P3 amplitude in change blindness.

Observers often miss visual changes in the environment when they co-occur with other visual disruptions. This phenomenon is called change blindness. Previous research has shown that change blindness increases with age. The aim of the current study was to explore the role of post-perceptual stimulus processing in age differences. Therefore, the P3 component of the event-related potential was measured while younger, middle-aged, and older participants performed a change detection task under different task demands. Older adults detected fewer changes than younger adults, even when the task was very easy. Detected changes elicited greater P3 amplitudes than undetected changes in younger adults. This effect was reduced or even absent for middle-aged and older participants, irrespective of task demands. Because this P3 effect is supposed to reflect participants' confidence in change detection, less confidence in own responses may explain the decline of change detection performance in normal aging.

Simon effects in change detection and change blindness.

Responses to centrally presented target stimuli are faster when they are accompanied by a task-irrelevant lateral accessory stimulus that corresponds spatially with the response hand (accessory variant of the Simon effect). In four experiments, we tested whether this effect depends on the awareness of the accessory stimulus. In a change blindness task, participants were asked to respond to a central letter that was accompanied by a lateral background change on some trials. Change blindness describes the phenomenon that even large changes may remain unnoticed when they occur simultaneously with another visual disruption, e.g., a blank screen. In a series of four experiments, a significant Simon effect was observed both when the accessory stimulus reached awareness and when it remained unnoticed. These results indicate that, based on the spatial location of an accessory stimulus, a spatial code is generated. This code interferes with the response code on the response-selection stage.

Violations of implicit rules elicit an early negativity in the event-related potential.

When participants are asked to learn letter strings, which were constructed on the basis of a complex rule system (an artificial grammar), they are able to classify novel letter strings as being grammatical or nongrammatical better than chance without explicit knowledge about the rules. We tested whether violations of such complex regularities can be detected by the brain, when strings were presented sequentially (i.e. letter by letter). Compared with regular letters, rule-violating letters elicited enlarged amplitudes of the N1 component in the event-related potential, indicating that violations are automatically detected by the brain. However, this effect occurred irrespective of the participants' classification of the strings, indicating that the brain's detection of regularity violations does not necessarily lead to correct classifications.

Is contextual cueing more than the guidance of visual-spatial attention?

When search displays are repeatedly presented, participants become faster in finding the target (contextual cueing, CC). It has been debated whether a more liberal response criterion might contribute to CC. In the current experiment, participants had to search through target-absent and target-present trials to compute d-prime as the measurement of sensitivity and beta as the measurement of response bias. Results showed that participants' sensitivity was not affected by the repetition of search displays. Although repeated displays led to both faster RTs and a more liberal response criterion, these effects were uncorrelated. In the event-related potential, RT effects were reflected by a late positive activity, which reflects response-related processes, but not by differences in the N2pc as electrophysiological correlate of focused attention. These results indicate that a more liberal response criterion is not the cause for CC effects in RTs but that other response-related processes might still contribute to the effect.

Contextual cueing effects despite spatially cued target locations.

Reaction times (RT) to targets are faster in repeated displays relative to novel ones when the spatial arrangement of the distracting items predicts the target location (contextual cueing). It is assumed that visual-spatial attention is guided more efficiently to the target resulting in reduced RTs. In the present experiment, contextual cueing even occurred when the target location was previously peripherally cued. Electrophysiologically, repeated displays elicited an enhanced N2pc component in both conditions and resulted in an earlier onset of the stimulus-locked lateralized readiness potential (s-LRP) in the cued condition and in an enhanced P3 in the uncued condition relative to novel displays. These results indicate that attentional guidance is less important than previously assumed but that other cognitive processes, such as attentional selection (N2pc) and response-related processes (s-LRP, P3) are facilitated by context familiarity.

Compatibility between stimulated eye, target location and response location.

Responses to stimuli are faster when the stimulus location spatially corresponds to the required response (standard Simon effect). Recently, a similar effect has been observed with monocular stimuli. Responses were faster when the response location and the stimulated eye corresponded (monocular Simon effect). It has been suggested that distinct mechanisms may underlie these two Simon effects. Here, we attempted to study these two mechanisms simultaneously. For mean reaction time, a finding of perfect additivity was obtained. These behavioral data coupled with surface electrophysiological measures support the view that two different mechanisms contribute independently to the monocular and standard Simon effect.

Cognitive processes facilitated by contextual cueing: evidence from event-related brain potentials.

Finding a target in repeated search displays is faster than finding the same target in novel ones (contextual cueing). It is assumed that the visual context (the arrangement of the distracting objects) is used to guide attention efficiently to the target location. Alternatively, other factors, e.g., facilitation in early visual processing or in response selection, may play a role as well. In a contextual cueing experiment, participant's electrophysiological brain activity was recorded. Participants identified the target faster and more accurately in repeatedly presented displays. In this condition, the N2pc, a component reflecting the allocation of visual-spatial attention, was enhanced, indicating that attention was allocated more efficiently to those targets. However, also response-related processes, reflected by the LRP, were facilitated, indicating that guidance of attention cannot account for the entire contextual cueing benefit.

Unvoluntary attentional capture in change blindness.

Change blindness occurs when the presentation of successively presented pictures goes along with a simultaneous presentation of distractors (e.g., mudsplashes). An ERP component (N2pc) was used to track shifts of attention to lateralized changes under different attentional conditions. Observing central changes and not knowing about lateral changes elicited no N2pc. If lateral changes were task relevant, however, an N2pc was observed for both detected and undetected changes. Repeating the first task, lateral changes also evoked an N2pc, although they were again not task relevant. These results indicate that the transient of the change, although never occluded by mudsplashes, did not attract attention (bottom up) automatically but additional knowledge about its occurrence is necessary (top down). An attentional shift, however, does not necessarily lead to an aware representation of the change.

Electrophysiological correlates of stimulus processing in change blindness.

Change blindness--the inability to detect salient changes when a distractor event occurs simultaneously--has been repeatedly used to investigate the neural correlates of awareness. The fact that the N2pc, which is basically assigned to attention processing, has been observed only for detected changes in such tasks lead to the assumption that this component may also reflect awareness. In contrast to previous electrophysiological studies, we used mudsplashes (experiment 1) or a very short blank (experiment 2) to induce change blindness so that the change was not occluded. A change, regardless of its detection, elicited a reliable N2pc. Successful change detection, however, was reflected in an enhanced amplitude of the N2pc component. Thus, the N2pc cannot be taken as a direct correlate of awareness but rather as a marker for a process that is necessary but not sufficient for awareness. Taking into account the generation of the N2pc in extrastriate visual areas, this finding fits nicely with the recent discussion about reentrant processing as a basis for visual awareness.

Localization of temporal preparation effects via trisected reaction time.

Previous research using nonchronometric measures in humans and animals has shown that warning signals can influence stages of processing throughout the reaction time (RT) interval. However, latency measures indicate that warning effects on RT are not due to the speeding of motor processes, at least not late ones. To better isolate the chronometric effects of temporal preparation, we used lateralized event-related potentials to divide mean RT into three time segments. Foreperiod duration had only a small, nonsignificant influence on the first and last segments (early visual and late motor processes, respectively). The chronometric effect was mainly restricted to the middle interval, which extended from onset of the N2pc component to onset of the lateralized readiness potential. The results imply that temporal preparation primarily speeds late perception, response selection or early motor processes.