Chaque saccade oculaire décale brusquement l'image projetée sur la rétine. Pourtant notre perception du monde reste stable et uniforme car le système visuel fait correspondre les informations avant et après chaque saccade. Pour établir cette correspondance, les mécanismes attentionnels seraient fondamentaux. Jusqu'à présent, ce lien transsaccadique a été mis en évidence par des études portant essentiellement sur le traitement des informations spatiales - à savoir, comment la position rétinienne d'un objet est corrigée à chaque saccade pour maintenir une perception stable du monde. Le traitement des traits visuels tels que la couleur ou la forme est encore mal compris et leur rôle dans l'impression de stabilité reste à établir. Est-ce que les traits et l'attention dédiée aux traits (feature-based attention), par définition indépendants de l'espace, participent aussi à la correspondance transsaccadique ? Pour analyser la relation entre le traitement des traits et celui des positions lors des saccades oculaires, cette thèse a suivi deux approches. La première s'est intéressée à la perception des attributs visuels, uniforme malgré l'hétérogénéité du système visuel. Les résultats ont montré que si la perception uniforme des attributs visuels s'appuie sur un apprentissage, les mécanismes sous-jacents ne seraient pas spécifiques aux mouvements oculaires. L'uniformité de la perception s'appuierait plutôt sur un mécanisme d'apprentissage associatif général. La seconde approche a cherché à mieux comprendre la nature de l'attention sélective transsaccadique. Les résultats ont montré que l'attention allouée à la cible d'une saccade ne contribue pas à aux mécanismes sélectifs guidés par les traits et engagés juste après l'exécution d'un mouvement oculaire. L'attention allouée à une cible saccadique et l'attention aux traits seraient alors indépendantes. Enfin, la dernière étude a montré que, lorsque l'attention sélective basée sur les traits est engagée pendant la préparation de la saccade en dehors de la cible saccadique, les traits sont maintenus pendant la saccade et affectent les processus sélectifs engagés juste après la saccade. L'attention transsaccadique ne serait alors pas de nature purement spatiale. L'ensemble de ces résultats suggère que les traits et l'attention aux traits joueraient un rôle dans la correspondance transsaccadique. / With each saccade, the image on the retina shifts abruptly but our perception of the surrounding world remains stable and uniform, because the visual system matches pre- and post-saccadic visual information. Attentional mechanisms could play a fundamental role in this process and numerous studies have examined the role of spatial attention. The processing of feature-based attention across saccades remains unclear and its role in matching pre- to post-saccadic visual information is not known. Do visual features and feature-based attention, assumed to enhance the feature-specific representations throughout the visual field, take part in the transsaccadic correspondence? To examine the relationship between feature and spatial processing, this thesis chose two approaches. The first one considered the uniform perception that we have for features despite the heterogeneity of the retina. Results show that, if the transsaccadic correspondence of visual features relies on learning, the underlying mechanisms would not be specific to eye movements. Visual constancy is more likely to arise from a general associative learning. The second approach examined the nature of transsaccadique attention. Results show that attention drawn to the saccade target did not contribute to selective mechanisms engaged just after an eye movement, suggesting a dissociation between feature-based attention and saccade programming. Finally, the last study show that feature-based selectivity is maintained across saccades to ensure spatiotopic correspondence, pointing out the potential role of feature-based attention in matching pre- to post-saccadic information.

The research domain on the Quality of Experience (QoE) of 2D video streaming has been well established. However, a new video format is emerging and gaining popularity and availability: VR 360-degree video. The processing and transmission of 360-degree videos brings along new challenges such as large bandwidth requirements and the occurrence of different distortions. The viewing experience is also substantially different from 2D video, it offers more interactive freedom on the viewing angle but can also be more demanding and cause cybersickness. Further research on the QoE of 360-videos specifically is thus required.The first goal of this thesis is to complement earlier research by (Tran, Ngoc, Pham, Jung, and Thank, 2017) testing the effects of quality degradation, freezing, and content on the QoE of 360-videos. The second goal is to test the contribution of visual attention as influence factor in the QoE assessment. Data will be gathered through subjective tests where participants watch degraded versions of 360-videos through an HMD with integrated eye-tracking sensors. After each video they will answer questions regarding their quality perception, experience, perceptual load, and cybersickness.Results of the first part show overall rather low QoE ratings and it decreases even more as quality is degraded and freezing events are added. Cyber sickness was found not to be an issue. The effects of the manipulation on visual attention were minimal. Attention was mainly directed by content, but also by surprising elements. The addition of eye-tracking metrics did not further explain individual differences in subjective ratings. Nevertheless it was found that looking at moving objects increased the negative effect of freezing events and made participants less sensitive for quality distortions. The results of this thesis alone are not enough to successfully regard visual attention as an influence factor in 360-video.

In second-hand e-commerce, categorization of new products is typically done by the seller. Automating this process makes it easier to upload ads and could lower the number of incorrectly categorized ads. Automatic ad categorization also makes it possible for a second-hand e-commerce platform to use a more detailed category system, which could make the shopping experience better for potential buyers. Product ad categorization is typically addressed as a text classification problem as most metadata associated with products are textual. By including image information, i.e. using a multimodal approach, better performance can however be expected. The work done in this thesis evaluates different multimodal deep learning models for the task of ad categorization on data from Blocket.se. We examine late fusion models, where the modalities are combined at decision level, and early fusion models, where the modalities are combined at feature level. We also introduce our own approach Text Based Visual Attention  (TBVA), which extends the image CNN Inception v3 with an attention mechanism to incorporate textual information. For all models evaluated, the text classifier fastText is used to process text data and the Inception v3 network to process image data. Our results show that the late fusion models perform best in our setting. We conclude that these models generally learn which of the baseline models to ’trust’, while early fusion and the TBVA models learn more abstract concepts. As future work, we would like to examine how the TBVA models perform on other tasks, such as ad similarity. / Produkter som läggs ut på marknadsplatser, såsom Blocket.se, kategoriseras oftast av säljaren själv. Att automatisera processen för kategorisering gör det därför både enklare och snabbare att lägga upp annonser och kan minska antalet produkter med felaktig kategori. Automatisk kategorisering gör det ocksåmöjligt för marknadsplatsen att använda ett mer detaljerat kategorisystem, vilket skulle kunna effektivisera sökandet efter produkter för potentiella köpare.Produktkategorisering adresseras ofta som ett klassificeringsproblem för text, eftersom den största delen av produktinformationen finns i skriftlig form. Genom att också inkludera produktbilder kan vi dock förvänta oss bättre resultat.I den här uppsatsen evalueras olika metoder för att använda både bild och text för annonsklassificering av data från blocket.se. I synnerhetundersökslate fusion modeller, där informationen från modaliteterna kombineras i samband med klassificeringen, samt early fusion modeller, där modaliteterna istället kombineras på en abstrakt nivå innan klassificeringen. Vi introduserar också vår egen modell Text Based Visual Attention (TBVA), en utvidgning av bildklassificeraren Inception v3 [1], som använder en attention mekanism för att inkorporera textinformation. För alla modeller som beskrivs i denna uppsats används textklassificeraren fast Text[2] för att processa text och bildklassificeraren Inception v3 för att processa bild. Våra resultat visar att late fusion modeller presterar bäst med vår data. I slutsatsen konstateras att late fusion modellerna lär sig vilka fall den ska 'lita' på text eller bild informationen, där early fusion och TBVA modellerna istället lär sig mer abstrakta koncept. Som framtida arbete tror vi det skulle vara av värde att undersöka hur TBVA modellerna presterar på andra uppgifter, såsom att bedöma likheter mellan annonser.

Infant visual attention develops rapidly over the first year of life, significantly altering the way infants respond to peripheral visual events. Here we present data from 5-, 7- and 10-month-old infants using the Infant Orienting With Attention (IOWA) task, designed to capture developmental changes in visual spatial attention and saccade planning. Results indicate rapid development of spatial attention and visual response competition between 5 and 10 months. We use a dynamic neural field (DNF) model to link behavioral findings to neural population activity, providing a possible mechanistic explanation for observed developmental changes. Together, the behavioral and model simulation results provide new insights into the specific mechanisms that underlie spatial cueing effects, visual competition, and visual interference in infancy.

<p dir="ltr">Automated Driving Systems (ADS) have evolved significantly over the past decade. With conditionally automated driving systems still requiring constant driver supervision and human intervention upon system request, a driver’s readiness to take over from an ADS has significant safety implications. Research suggests that drivers using ADS are more likely to engage in non-driving-related tasks (NDRTs), and this engagement can deteriorate takeover performance. However, different NDRTs can involve engagement of physical, visual and/or cognitive resources, which all can affect the takeover process in different ways. The potential interaction effects among these factors may be the cause of mixed empirical findings regarding the influence of NDRT engagement on takeover readiness and performance. Additionally, with more advanced ADS, takeover scenarios are likely to be less urgent. Yet, the ways in which drivers behave in response to a takeover request to intervene during such less urgent scenarios while engaged in NDRTs is still not well understood.</p><p dir="ltr">The purpose of this dissertation is to provide a better understanding of drivers’ response behavior during a conditionally automated vehicle takeover process by analyzing drivers’ motor, visual, and cognitive readiness in response to a takeover request (TOR). The work was completed in two phases. The first phase focused on the effects of pre-takeover visual engagement on takeover readiness in urgent situations. Two experiments were conducted as part of this first phase. Particularly, Study 1 investigated drivers’ post-TOR visual attention allocation and cognitive readiness after continuous visual NDRT engagement before a TOR. Study 2 examined drivers’ pre-TOR visual attention allocation and takeover performance both during and after voluntary engagement with visual NDRTs. The second phase used a non-urgent takeover scenario to investigate drivers’ takeover behavior and visual attention allocation when prioritizing the engagement of visual-manual NDRTs that differed in terms of cognitive engagement levels.</p><p dir="ltr">Study 1 required continuous visual attention in NDRTs and manipulated only the location of visual attention before an auditory TOR. Dependent measures included duration, location, and directness eye-tracking measures after the TOR, as well as freeze-probe cognitive readiness scores. Overall, delayed visual attention re-allocation in the driving scene, less dispersed gaze patterns, and worse perception and comprehension of road hazards were associated with off-road visual NDRT engagement. In addition, no significant benefit of enforcing on-road visual attention before the TOR, compared to the baseline condition without NDRT requirements, were found. These findings highlight the need to investigate the effects of more naturalistic NDRT engagement on takeover attention reallocation and takeover performance.</p><p dir="ltr">Study 2 complemented Study 1 by allowing voluntary switching of visual attention between the NDRT and the driving scene prior to the TOR, with the driving task being a priority. In addition, Study 2 investigated drivers’ takeover quality and understanding of the takeover scene using the appropriateness of their takeover decisions. Dependent measures were pre- and post-takeover eye-tracking measures, aligning to those used in Study 1, in addition to motor response measures, longitudinal and lateral vehicle control measures, and decisions made in response to a road obstacle. Overall, the driver’s post-TOR behaviors were not significantly affected by NDRT conditions, but visual NDRT-induced differences in gaze distribution were associated with the appropriateness of takeover decisions.</p><p dir="ltr">Finally, Study 3 used knowledge from prior studies to isolate the effects of different levels of cognitive engagement in real-world visual-manual NDRTs. The purpose was to investigate the effects of cognitive engagement on drivers’ visual attention allocation before and during the takeover, as well as on takeover performance in non-urgent takeover scenarios, where NDRT engagement was a priority. Dependent measures included eye-tracking measures, takeover response time, and vehicle control measures, used in prior studies. In summary, engagement in NDRTs with higher levels of cognitive engagement resulted in significant differences in pre-TOR visual attention allocation and less stable takeover maneuvers.</p><p dir="ltr">The findings from this work contribute to a better understanding of the effects of different components of NDRT engagement on takeover performance in conditionally automated driving systems. Ultimately, this work can contribute to improving the design of next-generation human-machine interfaces in surface transportation, including driver monitoring systems and in-vehicle displays, that promote safer human-automation integration in future ADS.</p>

Pendant les opérations de vol, les pilotes sont exposés à une variété de conditions émotionnelles, mentales et physiques qui peuvent affecter leurs performances et leur attention. Par conséquent, il est crucial de surveiller leur charge de travail et leurs niveaux d'attention pour maintenir la sécurité et l'efficacité de l'aviation, notamment dans les situations d'urgence. La charge de travail fait référence aux exigences cognitives et physiques imposées aux pilotes lors d'un vol. Des niveaux élevés de charge de travail peuvent entraîner une fatigue mentale, une attention réduite et une surcharge cognitive, ce qui peut entraver leur capacité à effectuer leurs tâches de manière efficace et efficiente. L'attention est un processus cognitif complexe qui limite la capacité de se concentrer et de comprendre tout en même temps. Dans les tâches de traitement de l'information visuelle, la vision humaine est la principale source du mécanisme d'attention visuelle. Le mode de distribution de l'attention d'un pilote a un impact significatif sur la quantité d'informations qu'il acquiert, car la vision est le canal le plus critique pour l'acquisition d'informations. Une mauvaise allocation des ressources attentionnelles peut amener les pilotes à négliger ou à oublier des paramètres spécifiques, ce qui entraîne des risques graves pour la sécurité des aéronefs. Ainsi, cette étude vise à étudier les niveaux d'attention des pilotes lors d'une procédure de décollage simulée, en mettant l'accent particulièrement sur les périodes critiques telles que les pannes de moteur. Pour ce faire, l'étude examine s'il existe une corrélation entre la dilatation de la pupille, mesurée à l'aide de la technologie de suivi oculaire, et les niveaux d'engagement, mesurés à l'aide de l'EEG. Les résultats indiquent que les changements de taille de la pupille sont effectivement corrélés aux changements d'activité de l'EEG, suggérant que la dilatation de la pupille peut être utilisée comme un indicateur fiable de l'engagement et de l'attention. Sur la base de ces résultats, la dilatation de la pupille et l'EEG peuvent être utilisés en combinaison pour examiner de manière globale le comportement des pilotes, car les deux mesures sont des indicateurs valides de l'engagement et de la charge cognitive. De plus, l'utilisation de ces mesures peut aider à identifier les périodes critiques où les niveaux d'attention des pilotes nécessitent une surveillance étroite pour garantir la sécurité et l'efficacité de l'aviation. Cette étude met en évidence l'importance de surveiller la charge de travail et les niveaux d'attention des pilotes et recommande d'utiliser les mesures de dilatation de la pupille et d'EEG pour évaluer la charge cognitive et l'engagement d'un pilote pendant les opérations de vol, améliorant ainsi la sécurité et l'efficacité de l'aviation. / During flight operations, pilots are exposed to a variety of emotional, mental, and physical conditions that can affect their performance and attention. Therefore, it is crucial to monitor their workload and attention levels to maintain aviation safety and efficiency, particularly in emergency situations. Workload refers to the cognitive and physical demands placed on pilots during a flight. High levels of workload can lead to mental fatigue, reduced attention, and cognitive overload, which can hinder their ability to perform their tasks effectively and efficiently. Attention is a complex cognitive process that limits the ability to focus and comprehend everything simultaneously. In visual information processing tasks, human vision is the primary source of the visual attention mechanism. A pilot's attention distribution mode significantly impacts the amount of information they acquire, as vision is the most critical channel for information acquisition. Improper allocation of attention resources can cause pilots to overlook or forget specific parameters, resulting in severe risks to aircraft safety. Thus, this study aims to investigate pilots' attention levels during a simulated takeoff procedure, with a specific focus on critical periods such as engine failures. To achieve this, the study examines whether there is a correlation between pupil dilation, measured using eye-tracking technology, and engagement levels, measured using EEG. The results indicate that changes in pupil size are indeed correlated with changes in EEG activity, suggesting that pupil dilation can be used as a reliable indicator of engagement and attention. Based on these findings, pupil dilation and EEG can be used in combination to comprehensively examine pilot behavior since both measures are valid indicators of engagement and cognitive workload. Furthermore, using these measures can help identify critical periods where pilots' attention levels require close monitoring to ensure aviation safety and efficiency. This study emphasizes the significance of monitoring pilots' workload and attention levels and recommends using pupil dilation and EEG measures to assess a pilot's cognitive workload and engagement during flight operations, ultimately enhancing aviation safety and efficiency.

No / Auditory signals have been shown to exert a marked influence on visual perception in a wide range of tasks. However, the mechanisms of these interactions are, at present, poorly understood. Here we present a series of experiments where a temporal cue within the auditory domain can significantly affect the localisation of a moving visual target. To investigate the mechanism of this interaction, we first modulated the spatial positional uncertainty of the visual target by varying its size. When visual positional uncertainty was low (small target size), auditory signals had little or no influence on perceived visual location. However, with increasing visual uncertainty (larger target sizes), auditory signals exerted a significantly greater influence on perceived visual location. We then altered the temporal profile of the auditory signal by modulating the spread of its Gaussian temporal envelope. Introducing this temporal uncertainty to the auditory signal greatly reduced its effect on visual localisation judgements. These findings support the view that the relative uncertainty in individual sensory domains governs the perceptual outcome of multisensory integration.

The present work represents an endeavour towards the investigation of the linguistic-cognitive system under the lenses of classical questions in cognitive and language sciences, by using a multi-method and question oriented approach. The ambition is to move a step towards the investigation of the mutual contribution of perceptual and linguistic-mediated representations to the understanding of human behaviour. Chapter 1 will expose the theoretical framework and the goals this project was set to achieve: contributing to the theoretical reconcile of visual attention and language functions, from a developmental perspective. Chapter 2 will expose the possibility to rethink the linguistic function as penetrating human cognition in a top-down fashion, and specifically, its influence on template-guided search and disengagement of attention mechanisms. Concurrently, chapter 3 will expose the possibility to rethink the role of visual attention as a useful tool, necessary to the computation of meaning: attention will be introduced as a window to investigate the influence of language-mediated representation (spoken and written) on visuospatial mechanisms by means of ERPs and eye-tracking methodology. Finally, chapter 4 will report the rationale and the interpretation of seven original experimental investigations of the word (and sentence) effect on perceptual representation during visuospatial tasks, across infants and adults. The final discussion will try to reconcile the results of the presented studies with the theoretical and methodological issues raised in the first, second and third chapters in an integrated perspective of a linguistic-cognitive system.

Le rôle de l’attraction des éléments extérieurs du point de vente physique demeure une problématique complexe pour les commerçants. De plus, l’expérience en point de vente physique est en pleine évolution, due en partie à une présence accrue des nouvelles technologies. Cette thèse répond à la problématique suivante : comment la vitrine du point de vente influence-t-elle l’expérience de magasinage anticipée ? Nous nous focalisons sur l’influence de la technologie interactive et du niveau de représentation (construal level) en vitrine sur la perception de l’atmosphère, les réponses attentionnelles, les réponses affectives, la valeur de magasinage anticipée et les intentions comportementales. Nous testons les effets modérateurs de la motivation de magasinage et de la tendance exploratoire du consommateur. Nous adoptons une approche hypothético-déductive et nous procédons à deux expérimentations afin de répondre à notre problématique.Les résultats de la première expérimentation in situ (n=251) révèlent un effet stimulant et hédonique de l’utilisation de la technologie interactive en vitrine. La deuxième expérimentation, en laboratoire (n=144), a mobilisé une méthode d’eye-tracking pour collecter les données sur l’influence du niveau de représentation des éléments en vitrine. Les résultats montrent une influence significative du niveau de représentation sur l’atmosphère globale perçue et sur les intentions comportementales. Les résultats des cartes de chaleur montrent que la motivation de magasinage utilitaire renforce l’attention visuelle sur les produits en vitrine. Aucun effet modérateur de la tendance exploratoire n’a été détecté dans les deux expérimentations. / One of the relevant issues for retailers in this dissertation is the role of marketing mix elements outside the physical store in attracting customers. Another relevant issue is the evolution of the physical retailing experience which is partly due to the ever increasing presence of new retail technology. The aim of this dissertation is to answer the following question: how do store windows influence anticipated shopping experience? We focus on the influence of interactive technology and construal level in store windows on perceived global atmosphere, visual attention, affective response, anticipated shopping value and patronage intentions. Shopping motivation and exploratory buying behavior tendency were tested for moderating effects. Two experiments were conducted for this doctoral research. The results from the in situ field experiment (n=251) reveal a hedonic and arousing effect from usage of the interactive window display. The second experiment on store window construal level (n=144) was conducted using eyeLtracking equipment in a controlled laboratory setting. The results show a significant influence of store window construal level on perceived global atmosphere and on patronage intentions. The results from the heat map analysis show that utilitarian shopping motivation reinforces visual attention to products in the window display. No moderating effect was found in either study for exploratory buying behavior tendency.

Die Suche nach einem Zielobjekt in einer komplexen visuellen Szene ist ein alltäglicher Wahrnehmungsvorgang und ein etabliertes experimentelles Paradigma für die Untersuchung selektiver Aufmerksamkeit. Einem klassischen Modell zufolge ist der Suchprozeß seriell: Die Objekte werden nacheinander vom Aufmerksamkeitsfokus selektiert und so für die Identifikation bereitgestellt. Ein Alternativmodell postuliert einen parallelen Suchprozeß, bei dem alle Objekte in der Szene gleichzeitig vom Sehsystem verarbeitet werden. Beide Modelltypen sind gleich gut mit den Resultaten bisheriger Verhaltensexperimente kompatibel. In der vorliegenden Arbeit wurden die neuronalen Grundlagen des Suchprozesses mit Hilfe der funktionellen Magnetresonanztomographie (fMRT) im menschlichen Gehirn untersucht. Es ist bekannt, dass das frontale Augenfeld (FEF) und drei Subregionen (AIPS, PIPS und IPTO) des posterioren parietalen Cortex (PPC) den im seriellen Suchmodell postulierten Teilprozeß der Verschiebung des Aufmerksamkeitsfokus (ohne Augenbewegungen) kontrollieren. In Experiment 1 wurde geprüft, ob diese Regionen auch am Suchprozeß beteiligt sind. Dazu wurde das fMRT-Signal zwischen einer schwierigen Suche nach einer Verknüpfung zweier visueller Merkmale und einer einfachen Suche nach einem einzelnen Merkmal verglichen. Motorische Anforderungen und Reizmuster waren in beiden Bedingungen so ähnlich wie möglich und in Kontrollexperimenten wurde sichergestellt, dass Aktivierungsunterschiede zwischen beiden Bedingungen keine motorischen oder sensorischen Prozesse reflektieren, sondern spezifisch den Prozeß der Verknüpfungssuche. FEF, AIPS, PIPS und IPTO wurden differentiell aktiviert. In Experiment 2 wurde getestet, ob die Beteiligung dieser Areale an der visuellen Suche von der Notwendigkeit einer Merkmalsverknüpfung abhängt. Dazu wurde eine schwierige Merkmalssuche mit der einfachen Merkmalssuche verglichen und kontrolliert, dass auch dieser Vergleich sensorische und motorische Faktoren eliminierte. Differentielle Aktivierungen in diesem Experiment reflektierten nun nicht mehr den Merkmalsverknüpfungsprozeß, sondern allein die höhere Schwierigkeit der Suche. Auch hier fand sich eine differentielle Aktivierung des FEF, AIPS, PIPS und IPTO. Dabei unterschieden sich die Schwierigkeit auf der Verhaltensebene wie auch die differentielle Aktivierung von PIPS auf der neuronalen Ebene nicht zwischen Verknüpfungs- und schwieriger Merkmalssuche. Die Ergebnisse demonstrieren, dass das FEF und drei Subregionen des PPC an der schwierigen visuellen Suche beteiligt sind. Dies ist gut mit der Annahme eines seriellen und nur schwer mit der eines parallelen Suchprozesses vereinbar. Darüber hinaus suggerieren die Befunde, dass der Beitrag des PPC und FEF zur visuellen Suche nicht auf den Prozeß der Merkmalsverknüpfung beschränkt ist, sondern allgemeiner die Anforderung an den Suchprozeß reflektiert. / The search for a target object in a complex visual scene is an all-day process of visual perception and an established experimental paradigm for the study of selective attention. A classical model postulates a serial search process. That is, objects are selected sequentially by the focus of attention and are thereby routed to the identification stage. An alternative model postulates a parallel search process, in which all objects within the scene are processed simultaneously. Both models are equally consistent with the current behavioural data. In this thesis, the neural basis of the search process in the human brain was investigated with functional magnetic resonance imaging (fMRI). The frontal eye field (FEF) and three sub-regions (AIPS, PIPS und IPTO) of the posterior parietal cortex (PPC) are known to control the shifting of the focus of attention in space (without eye movements), which is postulated by the serial model to be an essential sub-process of visual search. Experiment 1 tested whether the same areas are also engaged in the search process. The fMRI signal was compared between a difficult search for a feature conjunction and an easy search for a single feature. Motor requirements and stimuli were as similar as possible across conditions and control experiments demonstrated that activation differences between conditions do not reflect sensory or motor factors, but rather the process of conjunction search. The FEF, AIPS, PIPS, and IPTO were differentially activated. Experiment 2 tested whether the involvement of these areas in visual search depends on the necessity for conjoining features. A difficult feature search was compared with the easy feature search. This comparison also eliminated sensory and motor factors according to control experiments. Differential activations in this experiment did not reflect the feature conjunction process, but only the higher search difficulty. Again, a differential activation of the FEF, AIPS, PIPS, and IPTO was found. The conjunction and the difficult feature search did not differ in their difficulty at the behavioral level as well as in PIPS activation strength at the neural level. The results show that the FEF and three PPC sub-regions contribute to difficult visual search. This is consistent with the assumption of a serial, but much less consistent with the assumption of a parallel, search process. Furthermore the results suggest that the contribution of the PPC and FEF to visual search is not restricted to the feature conjunction process, but more generally reflects the demands on the search process.