Hinze Hogendoorn

Is this hand for real? attenuation of the rubber hand illusion by transcranial magnetic stimulation over the inferior parietal lobule

In the rubber hand illusion (RHI), participants incorporate a rubber hand into a mental representation of ones body. This deceptive feeling of ownership is accompanied by recalibration of the perceived position of the participants real hand toward the rubber hand. Neuroimaging data suggest involvement of the posterior parietal lobule during induction of the RHI, when recalibration of the real hand toward the rubber hand takes place. Here, we used off-line low-frequency repetitive transcranial magnetic stimulation (rTMS) in a double-blind, sham-controlled within-subjects design to investigate the role of the inferior posterior parietal lobule (IPL) in establishing the RHI directly. Results showed that rTMS over the IPL attenuated the strength of the RHI for immediate perceptual body judgments only. In contrast, delayed perceptual responses were unaffected. Furthermore, ballistic action responses as well as subjective self-reports of feeling of ownership over the rubber hand remained unaffected by rTMS over the IPL. These findings are in line with previous research showing that the RHI can be broken down into dissociable bodily sensations. The illusion does not merely affect the embodiment of the rubber hand but also influences the experience and localization of ones own hand in an independent manner. Finally, the present findings concur with a multicomponent model of somatosensory body representations, wherein the IPL plays a pivotal role in subserving perceptual body judgments, but not actions or higher-order affective bodily judgments.

High temporal resolution decoding of object position and category

We effortlessly and seemingly instantaneously recognize thousands of objects, although we rarely--if ever--see the same image of an object twice. The retinal image of an object can vary by context, size, viewpoint, illumination, and location. The present study examined how the visual system abstracts object category across variations in retinal location. In three experiments, participants viewed images of objects presented to different retinal locations while brain activity was recorded using magnetoencephalography (MEG). A pattern classifier was trained to recover the stimulus position (Experiments 1, 2, and 3) and category (Experiment 3) from the recordings. Using this decoding approach, we show that an objects location in the visual field can be recovered in high temporal resolution (5 ms) and with sufficient fidelity to capture topographic organization in visual areas. Experiment 3 showed that an objects category could be recovered from the recordings as early as 135 ms after the onset of the stimulus and that category decoding generalized across retinal location (i.e., position invariance). Our experiments thus show that the visual system rapidly constructs a category representation for objects that is invariant to position.

How many motoric body representations can we grasp

At present there is a debate on the number of body representations in the brain. The most commonly used dichotomy is based on the body image, thought to underlie perception and proven to be susceptible to bodily illusions, versus the body schema, hypothesized to guide actions and so far proven to be robust against bodily illusions. In this rubber hand illusion study we investigated the susceptibility of the body schema by manipulating the amount of stimulation on the rubber hand and the participant’s hand, adjusting the postural configuration of the hand, and investigating a grasping rather than a pointing response. Observed results showed for the first time altered grasping responses as a consequence of the grip aperture of the rubber hand. This illusion-sensitive motor response challenges one of the foundations on which the dichotomy is based, and addresses the importance of illusion induction versus type of response when investigating body representations.

Spatial coding and invariance in object-selective cortex

The present study examined the coding of spatial position in object selective cortex. Using functional magnetic resonance imaging (fMRI) and pattern classification analysis, we find that three areas in object selective cortex, the lateral occipital cortex area (LO), the fusiform face area (FFA), and the parahippocampal place area (PPA), robustly code the spatial position of objects. The analysis further revealed several anisotropies (e.g., horizontal/vertical asymmetry) in the representation of visual space in these areas. Finally, we show that the representation of information in these areas permits object category information to be extracted across varying locations in the visual field; a finding that suggests a potential neural solution to accomplishing translation invariance.

The speed of visual attention: what time is it?

The time course of visual attention has been studied using a number of experimental designs. Here, we present a refined version of a technique first used by Wundt more than a century ago and demonstrate it as an effective method to measure the speed of visual attention. The method generates precise and robust data quickly and is flexible enough to be adapted into a variety of established paradigms. In the experiment, participants view an array of moving clocks and report the time on a target clock, which was indicated by a peripheral or central cue. We found latencies of around 140 ms when the target was cued peripherally and latencies of around 240 ms when the target was cued centrally. These values are in good agreement with previous literature and support the validity of the technique as a way to measure the speed of visual attention.

The time course of attentive tracking.

The temporal characteristics of attentive tracking were studied in three experiments. We measured attentional dwell time and shift time during attentive tracking and showed that when an external cue is available, attention can repeatedly shift between items remarkably quickly. However, because attention is synchronized to this external cue, the time cost of shifting attention is inversely related to tracking rate. Furthermore, we show that during tracking, attentional shifts are likely synchronized to cue onsets rather than offsets. Results are discussed in the framework of a smoothly moving attentional spotlight.

Timing divided attention

This research was supported by a Pioneer grant from the Netherlands Visual attention can be divided over multiple objects or locations. However, there is no single theoretical framework within which the effects of dividing attention can be interpreted. In order to develop such a model, here we manipulated the stage of visual processing at which attention was divided, while simultaneously probing the costs of dividing attention on two dimensions. We show that dividing attention incurs dissociable time and precision costs, which depend on whether attention is divided duringmonitoring or duringaccess. Dividing attention during monitoring resulted in progressively delayed access to attended locations as additional locations were monitored, as well as a one-off precision cost. When dividing attention during access, time costs were systematically lower at one of the accessed locations than at the other, indicating that divided attention during access, in fact, involves rapid sequential allocation of undivided attention. We propose a model in whichdivided attention is understood as the simultaneous parallel preparation and subsequent sequential execution of multiple shifts ofundivided attention. This interpretation has the potential to bring together diverse findings from both the divided-attention and saccade preparation literature and provides a framework within which to integrate the broad spectrum of divided-attention methodologies.

Perceptual integration without conscious access

Significance Our brain constantly selects salient and/or goal-relevant objects from the visual environment, so that it can operate on neural representations of these objects, but what is the fate of objects that are not selected? Are these discarded so that the brain only has an impoverished nonperceptual representation of them, or does the brain construct perceptually rich representations, even when objects are not consciously accessed by our cognitive system? Here, we answer that question by manipulating the information that enters into awareness, while simultaneously measuring cortical activity using EEG. We show that objects that do not enter consciousness can nevertheless have a neural signature that is indistinguishable from perceptually rich representations that occur for objects that do enter into conscious awareness. The visual system has the remarkable ability to integrate fragmentary visual input into a perceptually organized collection of surfaces and objects, a process we refer to as perceptual integration. Despite a long tradition of perception research, it is not known whether access to consciousness is required to complete perceptual integration. To investigate this question, we manipulated access to consciousness using the attentional blink. We show that, behaviorally, the attentional blink impairs conscious decisions about the presence of integrated surface structure from fragmented input. However, despite conscious access being impaired, the ability to decode the presence of integrated percepts remains intact, as shown through multivariate classification analyses of electroencephalogram (EEG) data. In contrast, when disrupting perception through masking, decisions about integrated percepts and decoding of integrated percepts are impaired in tandem, while leaving feedforward representations intact. Together, these data show that access consciousness and perceptual integration can be dissociated.

Voluntary saccadic eye movements ride the attentional rhythm

Visual perception seems continuous, but recent evidence suggests that the underlying perceptual mechanisms are in fact periodic—particularly visual attention. Because visual attention is closely linked to the preparation of saccadic eye movements, the question arises how periodic attentional processes interact with the preparation and execution of voluntary saccades. In two experiments, human observers made voluntary saccades between two placeholders, monitoring each one for the presentation of a threshold-level target. Detection performance was evaluated as a function of latency with respect to saccade landing. The time course of detection performance revealed oscillations at around 4 Hz both before the saccade at the saccade origin and after the saccade at the saccade destination. Furthermore, oscillations before and after the saccade were in phase, meaning that the saccade did not disrupt or reset the ongoing attentional rhythm. Instead, it seems that voluntary saccades are executed as part of an ongoing attentional rhythm, with the eyes in flight during the troughs of the attentional wave. This finding for the first time demonstrates that periodic attentional mechanisms affect not only perception but also overt motor behavior.

Decoding the motion aftereffect in human visual cortex.

In the motion aftereffect (MAE), adapting to a moving stimulus causes a subsequently presented stationary stimulus to appear to move in the opposite direction. Recently, the neural basis of the motion aftereffect has received considerable interest, and a number of brain areas have been implicated in the generation of the illusory motion. Here, we use functional magnetic resonance imaging in combination with multivariate pattern classification to directly compare the neural activity evoked during the observation of both real and illusory motions. We show that the perceived illusory motion is not encoded in the same way as real motion in the same direction. Instead, suppression of the adapted direction of motion results in a shift of the population response of motion sensitive neurons in area MT+, resulting in activation patterns that are in fact more similar to real motion in orthogonal, rather than opposite directions. Although robust motion selectivity was observed in visual areas V1, V2, V3, and V4, this MAE-specific modulation of the population response was only observed in area MT+. Implications for our understanding of the motion aftereffect, and models of motion perception in general, are discussed.