Implicitly learning when to be ready: From instances to categories

There is growing appreciation for the role of long-term memory in guiding temporal preparation in speeded reaction time tasks. In experiments with variable foreperiods between a warning stimulus (S1) and a target stimulus (S2), preparation is affected by foreperiod distributions experienced in the past, long after the distribution has changed. These effects from memory can shape preparation largely implicitly, outside of participants’ awareness. Recent studies have demonstrated the associative nature of memory-guided preparation. When distinct S1s predict different foreperiods, they can trigger differential preparation accordingly. Here, we propose that memory-guided preparation allows for another key feature of learning: the ability to generalize across acquired associations and apply them to novel situations. Participants completed a variable foreperiod task where S1 was a unique image of either a face or a scene on each trial. Images of either category were paired with different distributions with predominantly shorter versus predominantly longer foreperiods. Participants displayed differential preparation to never-before seen images of either category, without being aware of the predictive nature of these categories. They continued doing so in a subsequent Transfer phase, after they had been informed that these contingencies no longer held. A novel rolling regression analysis revealed at a fine timescale how category-guided preparation gradually developed throughout the task, and that explicit information about these contingencies only briefly disrupted memory-guided preparation. These results offer new insights into temporal preparation as the product of a largely implicit process governed by associative learning from past experiences.

Implicitly learning when to be ready: from instances to categories

[Manuscript submitted for review]There is growing appreciation for the role of long-term memory in guiding temporal preparation. In experiments with variable foreperiods between a warning stimulus (S1) and a target stimulus (S2), preparation is affected by foreperiod distributions experienced in the past, long after the distribution has changed. Such memory-guided preparation shapes preparation largely implicitly and outside of a participants’ control. Recent studies have demonstrated the associative nature of such memory-guided preparation. When distinct S1s predict different foreperiods, they can trigger dissociative preparation accordingly. Here, we demonstrate that memory-guided preparation allows for another key feature of learning: the ability to generalize across acquired associations and apply them to novel situations. Participants completed a foreperiod task where S1 was a unique image of either a face or a scene on each trial. Images of either category were paired with different distributions with predominantly shorter versus predominantly longer foreperiods. Participants displayed dissociative preparation to never-before seen images of either category, without being aware of the predictive nature of these categories. They continued doing so in a subsequent transfer phase, after they had been informed that these contingencies no longer held. A novel rolling regression analysis revealed at a fine timescale how category-guided preparation gradually developed throughout the task, and illustrated how instructions at the start of the transfer phase interacted with these influences from long-term memory. These results offer new insights into temporal preparation as the product of a largely implicit process governed by associative learning from past experiences.

Dopamine and the elements of incentive learning

Dopamine and the elements of incentive learning explains how, in lever pressing for food tasks, incentive learning produces a gradient of attractiveness of environment stimuli: during magazine training, food activates dopaminergic neurons and the click and food cup become conditioned incentive stimuli, acquiring the ability to elicit approach and other responses; during lever-press training, the click activates dopaminergic neurons and the lever and lever-related stimuli become conditioned incentive stimuli. In conditioned place preference, amphetamine enhances dopaminergic neurotransmission and stimuli paired with amphetamine become conditioned incentive stimuli. In conditioned activity experiments, test-box stimuli paired with a dopamine-enhancer, e.g., cocaine, produce greater activity revealing incentive learning. In conditioned avoidance, the offset of an aversive warning stimulus putatively activates dopaminergic neurons leading safety-related stimuli to become conditioned incentive stimuli. If trained animals are treated with a dopamine receptor blocker, the initially intact ability of conditioned incentive stimuli to control responding declines over trials.

Changing the “When” and “What” of Intended Actions

Humans often have to modify the timing and/or type of their planned actions on the basis of new sensory information. In the present experiments, participants planned to make a right index finger keypress 3 s after a warning stimulus but on some trials were interrupted by a temporally unpredictable auditory tone prompting the same action ( experiment 1) or a different action ( experiment 2). In experiment 1, by comparing the reaction time (RT) to tones presented at different stages of the preparatory period to RT in a simple reaction time condition, we determined the cost of switching from an internally generated mode of response production to an externally triggered mode in situations requiring only a change in when an action is made (i.e., when the tone prompts the action at a different time from the intended time of action). Results showed that the cost occurred for interruption tones delivered 200 ms after a warning stimulus and remained relatively stable throughout most of the preparatory period with a reduction in the magnitude of the cost during the last 200 ms prior to the intended time of movement. In experiment 2, which included conditions requiring a change in both when and what action is produced on the tone, results show a larger cost when the switched to action is different from the action being prepared. We discuss our results in the light of neurophysiological experiments on motor preparation and suggest that intending to act is accompanied by a general inhibitory mechanism preventing premature motor output and a specific excitatory process pertaining to the intended movement. Interactions between these two mechanisms could account for our behavioral results.

Warning Signals Induce Automatic EMG Activations and Proactive Volitional Inhibition: Evidence From Analysis of Error Distribution in Simple RT

Typical simple reaction-time (RT) paradigms usually include a warning signal followed by a variable foreperiod before the presentation of a reaction stimulus. Most current interpretations suggest that the warning stimulus alerts the organism and so results in faster processing of either the sensory or motor components of the task. In this study, electromyography (EMG) was used to detect both covert and overt motor errors in a simple warned RT task. Results show that warning signals may trigger automatic motor activations that are likely to cause false alarms. Distribution analysis reveals that 77% of all errors detected with EMG are erroneous responses to the warning signal. Accordingly, we propose that movement triggering needs to be temporarily inhibited before the stimulus to prevent premature responses during the foreperiod. This proactive inhibition would be responsible for a paradoxical increase in RT for conditions with short foreperiods compared with control conditions in which no warning signal is presented. These results call for a reassessment of the theoretical framework used to interpret the effects of warning signals.

Early Contingent Negative Variation (CNV) Shows a Small Symmetrical Negativity in a Somatosensory Paradigm

The influence of sensory modulation on the early stage of information processing was investigated with a somatosensory contingent negative variation (CNV) paradigm. Whether or not even a somatosensory input as well as auditory or visual stimulus to one hemisphere elicits the symmetrical “early CNV” was also examined. Eleven normal individuals (3 males, 8 females) performed a conventional CNV paradigm with a click sound as the warning stimulus (WS) and a red light flash as the imperative stimulus (IS). Nine individuals (5 males, 4 females) did the somatosensory CNV paradigm with paired electrical stimuli as WS and IS. The subjects were instructed to press a button in response to IS as fast as possible. The early CNV amplitude was smaller and P300 latency was longer in somatosensory paradigm than conventional paradigm. In addition, the latency of P100 in a somatosensory paradigm was longer than that of N100 in a conventional paradigm. These findings suggest that the initiation of early detection, reflected by P100, the initiation of cognition, reflected by P300, and orienting response, reflected by early CNV, are delayed in a somatosensory CNV paradigm. Furthermore, all event-related potentials (ERPs) evoked by somatosensory stimuli showed a bilateral symmetry.

Smoking/Nicotine Affects the Magnitude and Onset of Lateralized Readiness Potentials

Smoking/nicotine improves cognitive performance for a variety of tasks. In most cases, reaction time (RT) is generally shorter after smoking/nicotine. While there may be some slight facilitation of stimulus-evaluation processing, most of the RT effects of nicotine appear to take place following the response-selection stage. This study investigated possible effects (in smokers) of smoking/nicotine on response preparation and execution processes using the lateralized readiness potential (LRP). On each trial, a warning stimulus preceded an imperative stimulus by 1.2s. The warning stimulus completely specified the correct response to the imperative stimulus. The study was completed in two morning sessions in which 4 cigarettes were smoked in each session. The nicotine yield of the cigarettes varied between sessions (0.05mg or 1.1mg). Maximum amplitudes of both the stimulus and response-locked LRPs were larger in the 1.1 mg session. For both stimulus- and response-locked LRPs, smoking the 1.1 mg cigarette (but not the 0.05 mg cigarette) shortened onset latency. However, the magnitude of the effect was much larger for the stimulus-locked LRPs, suggesting that response preparation is facilitated by smoking/nicotine to a greater degree than response execution.