Unconsciously registered items reduce working memory capacity.

The assumption that the contents of consciousness correspond to those of working memory (WM) is challenged by evidence that stimuli masked from awareness can be retained for several seconds (Soto et al., 2011; Bergström & Eriksson, 2015). To assess whether conscious and unconscious items compete in a unitary WM store we conducted an experiment in which some of the memory items in an array were masked from conscious sight using continuous flash suppression (CFS) while others remained visible. After a retention interval, participants decided whether the probed item (either masked or visible) had changed its orientation. Behavioral results indicated that change detection for visible items was significantly impaired when masked items were present, suggesting that masked items either displaced or reduced the precision of visible items in WM. However, change detection for masked items was at chance levels, indicating that these items were not stored. The unsuccessful attempt to encode them may have drawn upon a common pool of attentional resources needed to retain or retrieve visible items. Contralateral Delay Activity, an EEG index of net WM load, failed to temporally localize this interference.

Learning to deal with delayed outcomes: EEG oscillatory and slow potentials during the prefeedback interval.

It is well established that the stimulus-preceding negativity (SPN) decreases in amplitude as a task is mastered, a phenomenon generally attributed to the reduction in anticipatory attention as feedback becomes less needed. Typically, the experiments supporting this assumption have used relatively short delays (<3 s). However, we found in a previous study that this decline in amplitude, although present during the 2.5-s prefeedback delay of a patterned key-pressing task, was absent with an 8-s delay. We reexamined this finding using a 6-s delay and found that the SPN diminished at frontal sites as participants learned a sequence of four keypress durations, but that this modulation was limited to the early half of the delay (maximum at 2 s). Decline of lateralized sensorimotor theta activity across trials was also limited to early portions of the delay. These findings suggest that processes other than anticipatory attention to feedback may be more relevant for explaining SPN diminution. Such processes could include adjustment and maintenance of action-outcome expectancies (e.g., forward models) during the prefeedback interval.

Attention to Monocular Images Bias Binocular Rivalry.

When monocular images cannot be fused, perception alternates between the two (or more) possible images. This phenomenon, binocular rivalry (BR), is driven by the physical properties of the stimuli (size, contrast, spatial frequency, etc.) but it can also be modulated by attention to features of one of the rival stimuli (Chong et al., 2005; Dieter et al., 2016) and by attentional demands independent of the BR assessment (Paffen et al., 2008). Instead of the perceptually demanding tasks previously used to bias BR, we designed a simple counting task. We monocularly presented a number of trials (around 10 min) with a set of symbols and asked participants to count them. We found that after this task, dominance durations decreased for the unattended channel, and did not change for the attended channel. The results parallel those of Paffen et al. (2008) and square nicely with Levelt's second proposition, suggesting that the counting task effectively increased the sensibility of one channel which led to increased strength of the images presented to that channel. Alternatively, the results could be explained assuming that the non-attended channel was inhibited during the counting task, and the inhibition was carried over to the BR task.

Altered predictive contextual processing of emotional faces versus abstract stimuli in adults with Autism Spectrum Disorder.

OBJECTIVES: We investigated the proposition that Autism Spectrum Disorder (ASD) is associated with predictive contextual processing deficits. METHODS: We recorded electroencephalography (EEG) in adults with ASD and controls during the performance of a predictive contextual processing task, using either triangles or emotional faces. Targets were preceded by either randomized sequences (R) or by sequences including a predictive sequence (P). RESULTS: ASD subjects showed an attenuated behavioral facilitation (P versus R) compared with controls (faces). P3b amplitudes of P, R and the predictive sequence (n-1) were attenuated in ASD compared with controls. However, the attenuation of n-1 was more pronounced during the processing of faces. Controls demonstrated shorter peak P3b latencies of P versus R, while this facilitation was absent in ASD subjects. ASD subjects demonstrated functional connectivity alterations during the processing of random (triangles and faces) and predicted targets (faces). These changes were associated with weaker, more randomised, functional connections between frontal and parietal regions in ASD. CONCLUSIONS: We found predictive contextual processing alterations in ASD, which were more pronounced during the processing of emotional faces compared with abstract stimuli. SIGNIFICANCE: We provide novel evidence for the proposition that ASD is associated with deficits of top-down predictions.

Changes in the stimulus-preceding negativity and lateralized readiness potential during reinforcement learning.

According to reinforcement learning theory, dopamine-dependent anticipatory processes play a critical role in learning from action outcomes such as feedback or reward. To better understand outcome anticipation, we examined variation in slow cortical potentials and assessed their changes over the course of motor-skill acquisition. Healthy young adults learned a series of precisely timed, key press sequences. Feedback was delivered at a delay of either 2.5 or 8 s, to encourage use of either the striatally mediated, habit learning system or the hippocampus-dependent, episodic memory system, respectively. During the 2.5-s delay, the stimulus-preceding negativity (SPN) was shown to decline in amplitude across trials, confirming previous results from a perceptual categorization task (Morís, Luque, & Rodríguez-Fornells, 2013). This falsifies the hypothesis that SPN reflects specific outcome predictions, on the assumption that the ability to make such predictions should improve as a task is mastered. An SPN was also evident during the 8-s delay, but it increased in amplitude across trials. At the conclusion of the 8-s but not the 2.5-s prefeedback interval, a reversed-polarity lateralized readiness potential (LRP) was noted. It was suggested that this might indicate maintenance of an action representation for comparison with the feedback display. If so, this would constitute the first direct psychophysiological evidence for a popular hypothetical construct in quantitative models of reinforcement learning, the so-called eligibility trace.

Prepulse inhibition and facilitation of the postauricular reflex, a vestigial remnant of pinna startle.

If the postauricular reflex (PAR) is to be used effectively in studies of emotion and attention, its sensitivity to basic modulatory effects such as prepulse inhibition and facilitation must be determined. Two experiments were carried out with healthy young adults to assess the effects of transient and sustained visual prestimuli on the pinna-flexion response to trains of startle probes. In the first experiment, participants passively viewed a small white square. It was displayed from 1,000 ms prior to onset of a train of noise bursts until the end of that train. Relative to no-prepulse control trials, PAR amplitude was inhibited, possibly due to the withdrawal of attentional resources from the auditory modality. In the second experiment, participants performed a visual oddball task in which irrelevant trains of startle probes followed most briefly displayed task stimuli (checkerboards). Prepulse inhibition was observed when a transient stimulus preceded the first probe at a lead time of 100 ms. Amplitude facilitation was observed at longer lead times. In addition to documenting the existence of prepulse inhibition and facilitation, the data suggest that the PAR is not elicited by visual stimuli, that temporal expectancy does not influence its amplitude or latency, and that this vestigial microreflex is resistant to habituation. Results are interpreted in light of a recent theory that the human PAR is a highly degraded pinna startle, in which the reflex arc no longer includes the startle center (nucleus reticularis pontis caudalis).

Modulation of eyeblink and postauricular reflexes during the anticipation and viewing of food images.

One of the goals of neuroscience research on the reward system is to fractionate its functions into meaningful subcomponents. To this end, the present study examined emotional modulation of the eyeblink and postauricular components of startle in 60 young adults during anticipation and viewing of food images. Appetitive and disgusting photos served as rewards and punishments in a guessing game. Reflexes evoked during anticipation were not influenced by valence, consistent with the prevailing view that startle modulation indexes hedonic impact (liking) rather than incentive salience (wanting). During the slide-viewing period, postauricular reflexes were larger for correct than incorrect feedback, whereas the reverse was true for blink reflexes. Probes were delivered in brief trains, but only the first response exhibited this pattern. The specificity of affective startle modification makes it a valuable tool for studying the reward system.

Decomposition of warning effects in Parkinson's disease.

Neutral warning signals speed voluntary reactions by reducing temporal uncertainty and by triggering a brief burst of arousal. We attempted to isolate the phasic arousal mechanism in people with Parkinson's disease (PD) using a clock display to minimize temporal uncertainty. In this condition, the speeding of responses in a color-discrimination task by an accessory stimulus was the fully equivalent to the effect in age-matched control subjects. This indicates preserved phasic arousal in PD. Temporal preparation based on warning cues also appeared to be normal. By contrast, in a condition with high temporal uncertainty, the accessory stimulus (an air puff to the foot) impaired accuracy for the patients but not the neurologically normal subjects. The data are consistent with the view that PD disrupts internal but not external control of alertness.

The nursing hypothesis: an evolutionary account of emotional modulation of the postauricular reflex.

The postauricular reflex (PAR) is anomalous because it seems to be potentiated during positive emotions and inhibited during negative states, unlike eyeblink and other components of the startle reflex. Two evolutionary explanations based on simian facial emotion expressions were tested. Reflexes were elicited while 47 young adult volunteers made lip pursing or grimacing poses and viewed neutral, intimidating, or appetitive photos. The PAR was enhanced during appetitive slides, but only as subjects carried out the lip-pursing maneuver. These results support the nursing hypothesis, which assumes that infant mammals instinctively retract their pinnae while nursing in order to comfortably position the head. Appetitive emotions prime the ear-retraction musculature, even in higher primates whose postauricular muscles are vestigial.

Visual working memory deficits in patients with Parkinson's disease are due to both reduced storage capacity and impaired ability to filter out irrelevant information.

Given that Parkinson's disease broadly affects frontostriatal circuitry, it is not surprising that the disorder is associated with a reduction of working memory. We tested whether this reduction is due to diminished storage capacity or impaired ability to exclude task-irrelevant items. Twenty-one medication-withdrawn patients and 28 age-matched control subjects performed a visuospatial memory task while their electroencephalograms were recorded. The task required them to remember the orientations of red rectangles within the half of the screen that was cued while ignoring all green rectangles. Behavioural and electroencephalogram measures indicated that patients with Parkinson's disease were impaired at filtering out distracters, and that they were able to hold fewer items in memory than control subjects. The results support recent suggestions that the basal ganglia help control access to working memory.

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.

Reciprocal modulation of eye-blink and pinna-flexion components of startle during reward anticipation.

Because expectancies play a central role in current theories of dopaminergic neuron function, it is important to develop measures of reward anticipation processes. In the present study, reflexogenic bursts of white noise were presented to 39 healthy young adults as they awaited rewards and punishments in a gambling-like task. The rewards were small pieces of chocolate; the punishments, segments of bitter-tasting banana peel. Consistent with prior research on affective valence, postauricular reflexes were larger prior to rewards than punishments, whereas the reverse was true for acoustic blink reflexes. We theorized that potentiation of the postauricular reflex prior to consuming appetizing food is related to the priming of ear-retraction musculature during nursing in our remote ancestors.

Event-related potentials and illusory conjunctions in the time domain

Potenciales evocados y conjunciones ilusorias en el dominio del tiempo. Los rasgos procedentes de estímulos presentados a una tasa alta en una única posición espacial (Presentación Rápida de Series Visuales, PRSV) pueden migrar formando combinaciones incorrectas o conjunciones ilusorias. Se han propuesto diversos modelos seriales y paralelos para explicar lageneración de este tipo de errores. Los resultados conductuales se ajustan mejor al modelo paralelo bifásico que a otros modelos seriales y paralelos.Sin embargo, no se han estudiado los correlatos psicofisiológicos que distinguen las combinaciones correctas de las conjunciones ilusorias. Nuestro objetivo aquí es recoger registros electrofisiológicos durante esta tarea para determinar el grado en que convergen con la evidencia procedente de los resultados conductuales. En una tarea de PRSV se pedía identificar la única palabra que aparecía en mayúsculas en una serie de palabras en minúsculas presentadas a una tasa de 12 ítems por segundo. Como en experimentos anteriores, se observaron más intrusiones desde ítems posttargetque desde ítems pre-target. Los resultados de potenciales evocados apoyan también más al modelo paralelo bifásico que al serial o a otros modelos paralelos, tal y como se refleja en la ondas diferenciales asociadas a las combinaciones correctas e incorrectas

Features from stimuli presented at a high rate in a single spatial position (Rapid Serial Visual Presentation, RSVP) can migrate forming a wrongcombination or illusory conjunction. Several serial and parallel models have been proposed to explain the generation of this type of errors. The behavioral results fit better the two-stage parallel model than other serial and parallel models. However, they have not been studied the psychophysiological correlates that distinguish successful bindings from Illusory Conjunctions. The goal here is to collect electrophysiological records during this task to determine the degree to which they converge withthe evidence from behavioral results. One RSVP task required to identify the only uppercase word in a stream of lowercase words at a rate of 12 items/sec. As in previous experiments, more intrusions from post-targetitems than from pre-target items were observed. The results from eventrelated potentials are also more supportive for the two-stage parallel modelthan for the serial or other parallel models, as reflected in the differential waves associated to correct and wrong combinations

A new method to assess eye dominance

People usually show a stable preference for one of their eyes when monocular viewing is required (‘sighting dominance’) or under dichoptic stimulation conditions (‘sensory eye-dominance’). Current procedures toassess this ‘eye dominance’ are prone to error. Here we present a new method that provides a continuous measure of eye dominance and overcomes limitations of previous procedures. We presented dichoptic streams of randomly selected alphanumeric characters at rates around 5 Hzand asked observers to detect a particular character. In most subjects, the dichoptic streams of letters did not perceptually overlap, instead many participants were never aware that two letters were always presented.Interocular differences in target detection were evident in most observers, thus targets presented to one eye were always detected while targets presented to the other eye were generally missed. These interoculardifferences (i.e., eye dominance), were normally distributed and showed high test-retest reliability

Un método nuevo para evaluar la dominancia ocular . Generalmente, las personas muestran una preferencia estable por uno de sus ojos cuando se requiere visión monocular o bajo condiciones de estimulación dicóptica. Los procedimientos tradicionales para evaluar esa preferencia o dominancia ocular están sujetos a errores. En este artículo presentamos un método queproporciona una medida continua de dominancia y supera muchas de las limitaciones que se encuentran en otros métodos. Nuestro método consiste en presentar, dicópticamente, series de caracteres alfanuméricosseleccionadas al azar, a una frecuencia alrededor de 5 Hz, y pedir al observador que detecte un carácter en particular dentro de la serie. La mayoría de los observadores no percibieron las letras presentadasdicópticamente como solapadas, sino una única letra de cada vez. Diferencias interoculares en detección de targets fueron obvias en la mayoría de los sujetos, de forma que los targets presentados a uno de losojos se detectaban con facilidad, mientras que los presentados al otro no se percibían. Las puntuaciones de dominancia ocular, o diferencia interocular,obtenidas con nuestro método muestran una distribución normal y una alta fiabilidad test-retest

Spatial compatibility between stimulated eye and response location.

It is assumed that the eye-of-origin information is restricted to the visual cortex. However, reactions to monocular stimuli are faster when the response location and the stimulated eye are ipsilateral (compatible trials) than when they are contralateral (incompatible trials). We investigated whether this spatial compatibility effect had the characteristics of the conventional visual Simon effect. We found that the size of the compatibility effect was constant throughout the reaction time distribution, and there were no electrophysiological signs of incorrect response activation. These results indicate that the spatial code derived from eye-of-origin information does not produce a transient activation of the spatially compatible response, but a more tonic influence on response selection. The results also show that monocular information can exert influence outside the visual cortex and that spatial codes can be produced in the absence of attention movements.

Chapter 13 Bilateral frontal leucotomy does not alter perceptual alternation during binocular rivalry.

When discrepant stimuli are presented to each eye and fusion is impossible, perception spontaneously oscillates between the two patterns (binocular rivalry). Functional MRI (fMRI) research identified a frontoparietal network in the right hemisphere associated with perceptual transitions, and it has been proposed that this network is at the origin of the perceptual alternations. Neuroimaging results, however, do not imply causality and lesion studies are needed. Here, we studied one patient who had most of the prefrontal cortex disconnected from the rest of the brain after a bilateral frontal leucotomy. His performance in two binocular rivalry tasks was indistinguishable from that of the controls. The results indicate that prefrontal cortex is unnecessary for perceptual alternations during binocular rivalry.

Psychophysiological evidence for impaired reward anticipation in Parkinson's disease.

OBJECTIVE: According to a widely held view, mesencephalic dopamine neurons mediate feedback-based learning by broadcasting an error signal that indexes the difference between anticipated and actual response-contingent reward. The present experiment tested whether impaired learning of a probabilistic classification task by individuals with Parkinson's disease (PD) is associated with abnormal reward expectation. METHODS: The stimulus-preceding negativity (SPN), a brain potential known to reflect anticipation of motivationally significant events, was compared for blocks in which subjects anticipated high or low monetary rewards and punishments. RESULTS: The SPN was reduced in amplitude in patients relative to controls in the high monetary incentive condition. Furthermore, whereas the SPN varied in size as a function of cue complexity for control subjects, it did not for patients. CONCLUSIONS: These results suggest that anticipatory processes within cortical portions of the reward system are impaired by PD. SIGNIFICANCE: These data support previous claims that the SPN offers an electrophysiological index of activity within cortical portions of the reward pathway, and that reinforcement-based learning is impaired in PD.

Which stages of processing are speeded by a warning signal?

This article reviews psychophysiological and behavioral studies that attempt to identify which stages of processing are speeded by a neutral warning signal (WS), that is to say, one that conveys no information about the nature of the imperative stimulus or the required response. Experiments involving the lateralized readiness potential (LRP) provide evidence against the widely held view that warning effects on reaction time (RT) are due to facilitation of low-level motor processes. Studies of modality-specific evoked potentials similarly rule out a locus within sensory-perceptual processing. It is concluded that the speeding of RT by a neutral WS is most likely due to nonspecific motor priming within an early phase of response selection. In addition, fast-guess responses, in which subjects choose a response without fully analyzing the stimulus, are assumed to contribute to warning effects.

Stimulus-response compatibility between stimulated eye and response location: implications for attentional accounts of the Simon effect.

One influential theory of the Simon effect, the attention-shift hypothesis, states that attention movements are the origin of spatial stimulus codes. According to this hypothesis, stimulus-response compatibility effects should be absent when attention shifts are prevented. To test this prediction, we used monocular patches of color that required left or right key-press responses. About half of the subjects could discriminate which eye was stimulated (in a subsequent task), and showed strong spatial compatibility effects between the stimulated eye and the response location. The other half of the subjects could not make a utrocular discrimination (i.e., they could not judge which eye had received monocular stimulation), but the pattern of results was the same: the fastest reaction times were observed when the stimulated eye corresponded spatially to the required response (i.e., a Simon effect). Since the subjects presumably did not move their attention (from the subject's point of view, the stimuli were presented centrally), our results indicate that spatial codes can be produced in the absence of attention shifts. These results also show that utrocular discrimination can be assessed via indirect measures that are much more sensitive than explicit measures.