Blocking of Stimulus Control in Children with Autism

The present study aimed to investigate the blocking of stimulus control in three children with autism. We used a go/no-go procedure in a standard blocking paradigm. In Phase 1, we established one of two sounds or colored squares as a discriminative stimulus for touching a tablet screen. In Phase 2, a colored square was added to the sound or a sound was added to the colored square in a stimulus compound. The discrimination training continued as in Phase 1. We subsequently tested discriminative control by each of the single stimuli separately and by the compounds. Finally, after testing with no programmed consequences, we reestablished the original discrimination and replicated the test of stimulus control. The results support previous experiments by demonstrating that the establishment of discriminative control by a second stimulus by adding it to a previously established discriminative stimulus in a compound was blocked by the earlier discrimination training in all three participants. We discuss procedural details that may be critical to avoid the blocking of stimulus control in the applied field, particularly with respect to the acquisition of skills that involve multiple stimuli, such as joint attention, social referencing, and bidirectional naming.

Effect of a context shift on the inverse base rate effect

The Inverse Base Rate Effect (IBRE; Medin and Edelson (1988)) is a non-rational behavioural phenomenon in predictive learning. In the IBRE, participants learn that a stimulus compound AB leads to one outcome and that another compound AC leads to a different outcome. Importantly, AB and its outcome are presented three times as often as AC (and its outcome). On test, when asked which outcome to expect on presentation of the novel compound BC, participants preferentially select the rarer outcome, previously associated with AC. This is irrational because, objectively, the common outcome is more likely. Usually, the IBRE is attributed to greater attention paid to cue C than to cue B, and so is an excellent test for attentional learning models. The current experiment tested a simple model of attentional learning proposed by Le Pelley, Mitchell, Beesley, George, and Wills (2016) where attention paid to a stimulus is determined by its associative strength. This model struggles to capture the IBRE, but a potential solution suggested by the authors appeals to the role of experimental context. In the present paper, we derive three predictions from their account concerning the effect of changing to a novel experimental context at test, and examine these predictions empirically. Only one of the predictions was supported, concerning the effect of a context shift on responding to a novel cue, was supported. In contrast, Kruschke (2001b)’s EXIT model, in which attention and associative strength can vary independently, captured the data with a high degree of quantitative accuracy.

Neural Correlates of the Inverse Base Rate Effect

The Inverse Base Rate effect (IBRE; Medin & Edelson, 1988) is a non-rational behavioral phenomenon in predictive learning. Canonically, participants learn that the AB stimulus compound leads to one outcome and that AC leads to another outcome, with AB being presented three times as often as AC. When subsequently presented with BC, the outcome associated with AC is selected preferentially, in opposition to the underlying base rates of the outcomes. While many potential explanations of the effect exist, an error-driven learning account (Kruschke, 2001b) is particularly influential. A key component of this account is prediction error, a concept previously linked to a number of brain areas including the anterior cingulate, the striatum and the dorsolateral prefrontal cortex. The present study is the first fMRI study to directly examine the IBRE. Activations were noted in the brain areas linked to prediction error, including the caudate body, the anterior cingulate cortex and the middle frontal gyrus. Analysing the difference in activations for singular key stimuli (B and C), as well as frequency matched controls, supports the predictions made by the error-driven learning account.

Temporal Averaging Across Stimuli Signaling the Same or Different Reinforcing Outcomes in the Peak Procedure

The present study examined factors that affect temporal averaging in rats when discriminative stimuli are compounded following separate training indicating the availability of reward after different fixed intervals (FI) on a peak procedure. One group of rats, Group Differential, learned that a flashing light stimulus signaled that one type of food pellet reward could be earned for lever pressing after an FI 5 s interval and that a second type of food pellet reward could be earned after an FI 20 s interval in the presence of a tone stimulus. A second group of rats, Group Non-Differential, was similarly trained except that both types of rewards were scheduled across flash and tone trials. When given non-reinforced flash + tone compound test trials the interval containing the maximal response rate was no different than on flash alone test trials, although some responding also appeared near the long FI time. After these FI contingencies were reversed (flash signaled FI 20 s and tone signaled FI 5 s), however, further compound test trials more clearly revealed a temporal averaging pattern in both groups. The peak interval was shifted to the right of the FI 5 stimulus. Moreover, Group Differential rats acquired the reversed discrimination somewhat more rapidly than Group Non-Differential rats, and in a final selective satiation test Group Differential rats responded less in later intervals after they had been sated on the FI 20 s reward. These data suggest that temporal averaging in stimulus compound tests occurs even when the stimuli being combined signal qualitatively different rewards, but that decreasing the value of one of those rewards can shift responding away from the relevant time interval in a selective satiation test. However, when an especially salient stimulus (e.g., flashing light) signals a short FI, rats tend to process the compound stimulus more in terms of its individual elements.

Subcortical mapping and monitoring during insular tumor surgery

Object The treatment of insular tumors is controversial. Surgical treatment is associated with a higher morbidity rate than other therapies. The present work presents a new method in which the descending motor pathways are monitored during surgery for insular tumors. Methods Intraoperative monitoring was performed in a combination of 2 techniques. The motor cortex was stimulated with a transcranial electrical stimulus. In addition, direct subcortical stimulation was performed with an electrical anodal monopolar stimulus. Compound motor action potentials (CMAPs) were recorded from target muscles. Results Fifteen patients were included in this preliminary study. Following transcranial stimulation, CMAPs were recorded in all cases. Subcortical stimulation was successful in 12 cases. Significant CMAP alterations were recorded in 5 patients. There were no false-negative results in the series. Conclusions The technique presented here is a safe method. It allows a quantitative monitoring of motor function and functional mapping of the pyramidal tract during insular surgery.

Higher-Order Conditioning and Sensory Preconditioning of a Taste Aversion with an Exteroceptive CS1

An exteroceptive stimulus compound (context) was employed as CS1 in higherorder conditioning (H-OC, Experiments I and II), and sensory preconditioning (SPC, Experiment III) of a saccharin (CS2) aversion in rats. The results indicated that aversions were established with the H-OC as well as with the SPC procedures. Stimulus generalization and first-order conditioning explanations were ruled out by appropriate controls. A CS1-extinction period, performed prior to testing, did not affect the H-OC aversion, whereas it reduced the SPC aversion at least partially. These findings imply that interoceptive (taste, nausea) and exteroceptive stimuli (context) are readily associable in rats. Implications of the resemblance between the SPC procedure and long-delay taste-aversion learning are discussed.

Stimulus “Fractionation” in Paired-Associate Learning

It has been suggested that Ss may use only a portion of the nominal stimulus as a cue in paired-associate learning. Non-overlapping consonant trigram stimuli were used in such learning with numerals as responses. When the pairs had been learned, individual letters were presented and Ss were required to respond with the appropriate number. Results support the hypothesis that Ss had learned to respond to only part of the stimulus compound. Responses to letters which had been in the initial and final positions in the trigrams were correct significantly more often than responses to medial letters.