Learning at any rate: action-effect learning for stimulus-based actions.

Recent studies reported converging evidence for action-effect associations if participants adopted an intention-based action control mode in free choice conditions, whereas no evidence for action-effect associations was found when participants adopted a stimulus-based mode in forced choice conditions. However, it is not yet clear whether action control modes moderate acquisition or usage of action-effect associations. In the present experiment, two groups of participants underwent an acquisition phase consisting of either free or forced choice key presses that produced irrelevant, but contingent effect tones. In a subsequent test phase, participants freely chose the key to press after former effect tones were presented. A reliable consistency effect resulted for both the groups, i.e. participants preferred the key that produced the irrelevant tone in the preceding acquisition phase. In combination with prior findings, this consistency effect suggests that usage, but not acquisition of action-effect associations depends on an intention-based action control mode.

Asymmetrical intermanual transfer of learning in a sensorimotor task.

We examined the influence of the hand employed in sensorimotor learning on the acquired sequence knowledge in a serial reaction time task. Right-handed subjects trained either with the dominant or with the nondominant hand sequences of finger postures in response to a corresponding stimulus sequence. In the course of training, they were repeatedly asked to switch to the opposite hand, either responding to the original stimulus sequence with nonhomologues fingers or to the mirror-ordered sequence of stimuli with homologues fingers. When the right hand was used at acquisition, transfer to the same stimulus sequence increased with practice. In contrast, when the left hand was trained, transfer to the homologues finger sequence increased with practice. The results indicate qualitative differences in the acquired sequence knowledge controlling the dominant and the nondominant arm systems.

RT patterns and chunks in SRT tasks: a reply to Jiménez (2008).

Previous research has shown that the formation of units or chunks contributes to sequence learning in serial reaction time (SRT) tasks (Koch & Hoffmann, Psychological Research 63:22-35, 2000). However, some of these results were assumed to be unrelated to sequence learning and to reflect preexistent response tendencies (Jiménez, Psychological Research 72:387-396, 2008). In the Experiment of this study, we aimed to evaluate this issue. One group of participants responded to a strongly structured sequence of digits by pressing one out of six response keys depending on digit identity. In a second experimental group, a weakly structured sequence was presented, which contained comparable transitions among the single items, but did not have series of ascending and descending triplets of successive digits. The results indicated that serial learning in general as well as response tendencies to certain fragments of the sequence were modulated by the manipulation of the strength of relational patterns. The data are consistent with the notion that relational patterns contribute to the formation of chunks as suggested in the original study.

Integrated and independent learning of hand-related constituent sequences.

In almost all daily activities fingers of both hands are used in coordinated succession. The present experiments explored whether learning in such tasks pertains not only to the overall sequence spanning both hands but also to the constituent sequences of each hand. In a serial reaction time task, 2 repeating hand-related sequences were intertwined, so that actions of one hand alternated with actions of the other hand. Integrated learning of the overall sequence was weak when the constituent sequences were uncorrelated (Experiment 1) and massive when they were correlated (Experiment 2). Both experiments yielded evidence suggesting partly independent learning of the hand-related sequences. There were no reliable indications of intermanual transfer of this hand-related sequence knowledge. The findings suggest that after sufficient training of coordinated action sequences involving several limbs, a part of the acquired sequence knowledge begins to be represented in an effector-specific manner.

Exploiting redundancy for flexible behavior: unsupervised learning in a modular sensorimotor control architecture.

Autonomously developing organisms face several challenges when learning reaching movements. First, motor control is learned unsupervised or self-supervised. Second, knowledge of sensorimotor contingencies is acquired in contexts in which action consequences unfold in time. Third, motor redundancies must be resolved. To solve all 3 of these problems, the authors propose a sensorimotor, unsupervised, redundancy-resolving control architecture (SURE_REACH), based on the ideomotor principle. Given a 3-degrees-of-freedom arm in a 2-dimensional environment, SURE_REACH encodes 2 spatial arm representations with neural population codes: a hand end-point coordinate space and an angular arm posture space. A posture memory solves the inverse kinematics problem by associating hand end-point neurons with neurons in posture space. An inverse sensorimotor model associates posture neurons with each other action-dependently. Together, population encoding, redundant posture memory, and the inverse sensorimotor model enable SURE_REACH to learn and represent sensorimotor grounded distance measures and to use dynamic programming to reach goals efficiently. The architecture not only solves the redundancy problem but also increases goal reaching flexibility, accounting for additional task constraints or realizing obstacle avoidance. While the spatial population codes resemble neurophysiological structures, the simulations confirm the flexibility and plausibility of the model by mimicking previously published data in arm-reaching tasks.

Unconscious priming according to multiple S-R rules.

The present study investigated if unconscious primes can be processed according to different stimulus-response (S-R) rules simultaneously. Participants performed two different S-R rules, such as judging a digit as smaller or larger than five and judging a letter as vowel or consonant. These S-R rules were administered in random order and announced by a previously presented cue. Each target stimulus was preceded by subliminal primes which afforded a different or an identical response according to either the currently irrelevant or currently relevant S-R rule. In three experiments, we consistently found priming effects according to currently irrelevant S-R rules, even when primes for the relevant and irrelevant S-R rules were presented simultaneously. Thus, unconscious stimuli have the power to activate responses according to currently required and currently not required S-R rules concurrently. The results are in line with response activation accounts of subliminal priming and suggest that at least two routes may gain access on response processes simultaneously.

Evidence for task-specific resolution of response conflict.

When a target requires different responses to a relevant and to an irrelevant task in a task-switching paradigm, there is response conflict. This target-induced response conflict was combined with conflict caused by a subliminally presented prime presented prior to the target. We found that target-related conflict reduced prime-induced conflict effects within the same trial However, target-related conflict modified prime-related conflict effects according to the irrelevant stimulus-response (S-R) rule, but not according to the relevant S-R rule. Moreover, trial-to-trial modulations of the target congruency effect were observed in task repetition trials, but not in task switch trials. These results indicate that conflict resolution mechanisms, at least under the present circumstances, operate in a strictly task-specific manner.

Selecting spatial frames of reference for visual target localization.

This study examined the selection of spatial frames of reference for target localization in visual search. Participants searched for local target characters in global character configurations. The local targets could be localized relative to the character configuration in which they were embedded or relative to the presentation screen on which the configurations were displayed. We investigated under which conditions the configurations, or the screen served as frame of reference for target localization. Three experiments revealed an increasing impact of screen-related target localization with decreasing spatial uncertainty of targets in screen-related coordinates. The results indicate the capability of the visual system to localize relevant visual stimuli with respect to those frames of reference that yield the most redundant spatial distribution of these stimuli.

Local contextual cuing in visual search.

Previous research has indicated that covariations between the global layout of search displays and target locations result in contextual cuing: the global context guides attention to probable target locations. The present experiments extend these findings by showing that local redundancies also facilitate visual search. Participants searched for randomly located targets in invariant homogenous displays, i.e., the global context provided information neither about the location nor about the identity of the target. The only redundancy referred to spatial relations between the targets and certain distractors: Two of the distractors were frequently presented next to the targets. In four of five experiments, targets with frequent flankers were detected faster than targets with rare flankers. The data suggest that this local contextual cuing does not depend on awareness of the redundant local topography but needs the redundantly related stimuli to be attended to.

Mixed signals? Morphological and molecular evidence suggest a color polymorphism in some neotropical polythore damselflies.

The study of color polymorphisms (CP) has provided profound insights into the maintenance of genetic variation in natural populations. We here offer the first evidence for an elaborate wing polymorphism in the Neotropical damselfly genus Polythore, which consists of 21 described species, distributed along the eastern slopes of the Andes in South America. These damselflies display highly complex wing colors and patterning, incorporating black, white, yellow, and orange in multiple wing bands. Wing colors, along with some components of the male genitalia, have been the primary characters used in species description; few other morphological traits vary within the group, and so there are few useful diagnostic characters. Previous research has indicated the possibility of a cryptic species existing in P. procera in Colombia, despite there being no significant differences in wing color and pattern between the populations of the two putative species. Here we analyze the complexity and diversity of wing color patterns of individuals from five described Polythore species in the Central Amazon Basin of Peru using a novel suite of morphological analyses to quantify wing color and pattern: geometric morphometrics, chromaticity analysis, and Gabor wavelet transformation. We then test whether these color patterns are good predictors of species by recovering the phylogenetic relationships among the 5 species using the barcode gene (COI). Our results suggest that, while highly distinct and discrete wing patterns exist in Polythore, these "wingforms" do not represent monophyletic clades in the recovered topology. The wingforms identified as P. victoria and P. ornata are both involved in a polymorphism with P. neopicta; also, cryptic speciation may have taking place among individuals with the P. victoria wingform. Only P. aurora and P. spateri represent monophyletic species with a single wingform in our molecular phylogeny. We discuss the implications of this polymorphism, and the potential evolutionary mechanisms that could maintain it.

Conscious control over the content of unconscious cognition.

Visual stimuli (primes) presented too briefly to be consciously identified can nevertheless affect responses to subsequent stimuli - an instance of unconscious cognition. There is a lively debate as to whether such priming effects originate from unconscious semantic processing of the primes or from reactivation of learned motor responses that conscious stimuli afford during preceding practice. In four experiments we demonstrate that unconscious stimuli owe their impact neither to automatic semantic categorization nor to memory traces of preceding stimulus-response episodes, but to their match with pre-specified cognitive action-trigger conditions. The intentional creation of such triggers allows actors to control the way unconscious stimuli bias their behaviour.

The impact of anticipated action effects on action planning.

Three experiments with a total of 72 participants investigated the assumption that motor actions are planned in terms of their sensorial effects. Participants had to prepare a certain action A that consistently led to a sensorial effect (a tone of certain pitch). Instead of (in Experiment 1) or before (in Experiments 2 and 3) the execution of the prepared action, another response B had to be carried out, which either resulted in the same or in a different auditory effect (a tone of same or different pitch). It was found that a to-be-executed response B was in general initiated more quickly when it resulted in the same effect as a concurrently prepared response A. The results are considered as evidence for the basic notion that the preparation and initiation even of very simple actions is mediated by an anticipation of their reafferences.

Psychology has to deal with efferences too.

The authors argue that F. Mechsner's (2004) perceptual-cognitive approach is an important contribution to the current discussion of motor control. Mechsner presents convincing evidence against direct motor control. Nevertheless, the mechanisms by which perceptual-cognitive representations determine efferent commands must still be clarified.

Stimulus-dependent modulation of perceptual and motor learning in a serial reaction time task.

In two experiments, we investigated the impact of spatial attributes on the representation acquired during a serial reaction time task. Two sequences were used, in which structural regularities occurred either in the horizontal or in the vertical locations of successive stimuli. After training with the dominant hand, participants were required to respond with the non-dominant hand to either the original sequence or to a mirror-ordered version of the original sequence that required finger movements homologous to those used during training. We observed that a difference in reaction times between the two transfer conditions was smaller in the vertical sequence than in the horizontal sequence. This pattern of results was independent of whether three fingers (Experiment 1) were used or only one finger (Experiment 2) was used for responding. This result suggests that perceptual and motor learning mechanisms may be weighted differently depending on the context in which the stimulus is presented.

Impact of instruction on the acquisition of sequence knowledge in a sensorimotor task.

We examined whether and to what extent a sequence of finger movements can be learned and transferred to the untrained hand according to the muscle homology depending on the relative salience of response locations and effectors. Participants performed a discrete sequence production task, in which they were asked to learn a sequence of either key locations or of finger movements. Each training block was followed by a transfer block in which responding with the opposite hand was required. Before the last transfer block participants received an unexpected instruction. They had to reproduce the sequence of key locations instead of the sequence of finger movements and conversely, the sequence of finger movements instead of the sequence of key locations. The results do not support the existence of a sequence representation for the order of finger movements irrespective of the hand used.

Response specific temporal expectancy: evidence from a variable foreperiod paradigm.

When a stimulus-response event is frequently paired with a specific foreperiod, response performance for this event is improved after this foreperiod. This phenomenon is referred to as specific temporal expectancy. In four experiments, we investigated whether stimulus- or response-related processing benefits from specific temporal expectancy. In a speeded choice reaction task, different features of the imperative stimuli were frequently paired with foreperiods in such a way that only in some experiments were the responses also frequently paired with foreperiods. Participants revealed evidence for specific temporal expectancy when responses were frequently paired with foreperiods, but not when only the stimuli were frequently paired with foreperiods. We concluded that specific temporal expectancy affects response-related processing.

The scope and precision of specific temporal expectancy: evidence from a variable foreperiod paradigm.

Recent evidence from choice response time experiments with variable foreperiods (FPs) has shown that temporal expectancy can be event specific. When a certain target appears particularly frequent after one certain FP, participants tend to expect that target after that FP. This typically results in best performance for that target when it appears after that FP. In the present study, we investigated how temporally precise event-specific temporal expectancy is, and in which range of FPs it can be found. Two target stimuli were asymmetrically distributed over two "peak-FPs" and were equally distributed over 13 additional FPs. Event-specific expectancies were found for peak-FP pairs of 500/1,100 ms and 300/500 ms. Furthermore, the event expectancies generalized to a wide range of nonpeak FPs surrounding the peak FPs.

The specificity of temporal expectancy: evidence from a variable foreperiod paradigm.

In speeded choice tasks with variable foreperiods (FPs), individuals behaviourally adapt to various frequency manipulations. Adaptations have been shown to frequencies of different stimulus-response events, to frequencies of different foreperiods, and to frequencies of different event-foreperiod combinations. We have investigated how participants adapt to a situation where all three frequency manipulations are done simultaneously. Three variable foreperiod experiments are reported. In Experiment 1, one target (the peak distributed target) appeared particularly frequently after one particular FP (the peak foreperiod), while another target was less frequent and equally distributed over all foreperiods. In Experiment 2, the equally distributed target was overall more frequent than the peak distributed one. In both experiments, performance advantages for the peak distributed target were specific to the peak foreperiod, and performance advantages at the peak foreperiod were specific to the peak distributed targets. A third experiment showed that, when two differently frequent target are both equally distributed over FPs, the performance distribution over FPs is not significantly different between both targets. Together, the results suggest that participants were able to simultaneously and specifically adapt to frequency manipulations in events, foreperiods, and event-foreperiod combinations.

Temporal cueing of target-identity and target-location.

In four experiments either a short or a long foreperiod preceded the presentation of one of two targets, presented either in the center of the screen (Experiment 1) or at one of two locations (Experiments 2-4). Participants were to identify the presented target by pressing a left or a right button as quickly as possible. In Experiment 1, each of the two targets and in Experiment 2, each of the two locations appeared frequently after one and infrequently after the other foreperiod. Experiments 3 and 4 explored the combined effects of disparate frequency distributions of targets and locations to the two foreperiods. Reaction times and error rates revealed faster processing and/or less errors for respectively those targets and locations which were frequent after the current foreperiod. The data suggest that besides location-specific target expectancies (Hoffmann & Kunde, 1999) also time-specific expectancies for those targets and target-locations are formed which are likely at the respective point in time.

Early and late selection in unconscious information processing.

In four experiments, we investigated whether masked stimuli in priming experiments are subjected to early or to late selection. In Experiment 1, participants classified four target-pictures as being small or large. In line with early selection accounts, prime-pictures with a different perceptual appearance as the experienced targets did not elicit congruency effect. In Experiment 2, 40 targets all depicting animals were presented. Results were in line with late selections assumptions because novel animal primes but not novel primes from different semantic categories yielded congruency effects. In Experiment 3, the targets were chosen such that there is a second semantic feature that covaried with the required response. Here, novel primes picturing small animals did not influence target responses with regard to the instructed size classification, but with regard to their affiliation to the category animal. In Experiment 4, small and large pictures from two categories were presented. Category match did not influence priming, ruling out that feature overlap contaminated the former results. The results indicate that participants' prestimulus expectations determine in which stage in the processing-stream masked stimuli are selected.