Progetto Di Ricerca
PROGETTO DI RICERCA
TITOLO: Altering spatial priority maps via reward-based learning: A combined behavioral and ERP approach.
PROPONENTE: Prof. Maurizio Codispoti
DURATA: 12 mesi
Introduction
To allow individuals to maximize gains (and reduce losses), the brain is endowed with the capacity of weighing positive/negative consequences of behavior and reorganizing through plasticity. Basic motivational systems are responsible for encoding the appetitive (positive) and aversive (negative) emotional valence of objects, events or contexts, together with their motivational relevance (intensity and arousal) [1-3]. The activation of motivational systems in turn modulates cognitive processes, such as attention and perception. For example, emotional scenes reflexively engage attentional resources to facilitate perception and ultimately promote adaptive behavior [4-7].
The influence exerted by motivational systems on behavior has long been addressed in traditional learning studies, leading to the general notion that different forms of learning rest on a more or less complex association of a given action (or ensemble of actions) with the obtainment of a reward or with the avoidance of an aversive event, or punishment [e.g. 8-12]. In other words, rewards (and punishments) play a major role in shaping behavior, inasmuch as they can be viewed as a critical drive and guide for the ability to learn from experience. Recent evidence established that not only behavior but also cognitive processes can be shaped by outcomes; specifically, visual selective attention can be shaped by the rewards obtained by the individual on past encounters with specific objects or contexts [13]. In essence, the controlled delivery of rewards in relation to low-level features (e.g. color) determines robust effects on the attentional priority of those features, both in the short- and long-term[e.g. 14-17].This work points to a critical link between reward and attention, with the first shaping (through learning) the setting of attentional priority in the brain.
Aim of the study/Hypothesis
The present projectaimsat investigating whether, by means of a suitable reward-based training protocol, we can produce enduring changes in saliency maps that are responsible for directing visuo-spatial attention; strikingly, thus far reward-based attentional learningin the spatial domain has never been reported. We expect these effects to manifest both behaviorally and as modulations of critical event-related potential (ERP) components, such as the N2pc component, a lateralized negative deflection assumed to reflect attentional selection of task-relevant stimuli or a combination of target selection and distractor suppression [e.g. 18-19].In addition, the project aims at unravel how reward-based attentional learning takes place. On the one hand, one could hypothesize that the appetitive valence of the delivered reward is transferredto the specific spatial position to which it has been associated, so that, following training, the processing of stimuli at that location will result in some degree of emotional activation (e.g.modulation of the Late Positive Potential; LPP), as if the location itself had acquired a positive emotional valence. On the other hand, one can hypothesize that the reward acts as a crucial leverage to enact the learning process, serving as a teaching signal [13]. If this were the case, a given spatial position would not acquire any emotional valence in itself - likely resulting in the absence of any modulations of late ERP components linked to emotional processing, but still its attentional priority will changethrough learning.
Materials and Methods
Theexperimental procedure will comprise a reward-based training, whereby specific spatial positions will be associated with a higher (or lower) probability of obtaining a positive outcome (high reward), and two tests sessions, one before and one after training, aimed at measuring the impact of reward-mediated learning in the allocation of spatial selective attention.
Participants. Forty healthy volunteers, right-handed, with normal or corrected-to-normal visual acuity,and naïve as to the purpose of the research,will be enrolled in the study.
Baseline/test task. A variant of a visual search task will be developed, in which participants will be required to search for one or two targets, amongst an array of 7 or 6 distractors, respectively. On each trial, after a fixation display, an iso-eccentric circular array of 8 stimuli (each within a white square marking spatial position) will be briefly presented (70ms), and immediately replaced by 8 identical masking patterns (consisting of overlapping distractors). The target stimuli will befour capital letters (F, G, M, D) and four digits (2, 4, 7, 9); distractors will be seven ASCII characters. Participants will be instructed to report all targets they can detect in the stimulus array. Single and double target conditions will be presented randomly, with no indication to the participants about the number of targets in the current trial. Targets will appear with the same frequency at all eight positions. Responses will be non-speeded and performance will be evaluated based on the accuracy of report. On a subset of trials, stimuli will be presented only in two positions, one for each hemifield; crucially, this simplified array(and in particular trials in which one of the two targets will be at a critical position - e.g. highly rewarded - and the other at a neutral one) will allow us to test whether a givencritical location has acquired an emotional valence following training (see above).
Training session task. Participants will be asked to locate a single target (present in all trials) amongst 7 distractors, and discriminate its internal structure. Targets will be made of two stacked triangles pointing upwards, either with a white triangle over a black triangle, or the reverse; the task of the participants will be to report the color of the upper triangle, by key press, as quickly and accurately as possible. Distractors will consist of two stacked triangles pointing downwards. Correct responses (but not errors) will be followed by a reward (shown at target position), which will be either high (10 points) or low (1 point), with the same overall probability.However, probability of earning high vs. low reward will vary across locations, based on a completely predetermined schedule. For two critical locations, high reward will be more likely (80% probability) than low reward; for two other critical locations, high reward will beless probable (20% probability) than low reward. For the remaining four locations (neutral), high and low rewards will be equally likely.Reward assignments to specific locations will be counterbalanced across subjects.
Procedure. Each participant will complete one baseline session and two training sessions on consecutive days and a test session after a four-day delay. Electrophysiological (EEG) recordingwill be obtained during the entire duration of both baseline and test sessions. ERPs will be analyzed in relation to targets presented at specific locations within the array, mainly focusing on the N2pc and LPP components, but also assessing eventual modulations of the P1, N1 and P3 components.
Expected results e theoretical/translational impact
We expect to be able to provide evidence that a suitablereward-based training can lead to long-lasting alterations in spatial priority maps, in turn affecting the ability of observers to locate and identify task-relevant information at different locations in the visual field. As a result of training with unbalanced probability to obtain high vs. low reward at the various locations, performance at test is expected to vary accordingly, with relatively higher (or lower) accuracy for locations more often associated with high (or low) reward, and congruent modulations of the critical ERP components; for example, an enhanced(or suppressed)N2pc is expected for targets at highly(or poorly)rewarded locations, respectively. Critically, we will also shed light on the specific role of reward in mediating learning, by directly testing whether itacts as a teaching signal for the enactment of the learning process [13], or whether it simply affectsthe attentional priority of a given location by tagging it with appetitive emotional valence, following a repeated association. In sum, the collected results will substantially advance current knowledge on the influence of rewards on attentional learning, and will also have broad implications in terms of translational applicability, including for the rehabilitative treatment of spatial deficits of attention.
References
[1] Berridge, K.C.Robinson, T.E. (2003). Parsing reward. Trends in Neuroscience, 26, 507-513.
[2] Rolls, E.T. (2000). Précis of The brain and emotion. Behavioral and Brain Sciences, 23, 177-191.
[3] Bromberg-Martin, E.S., Matsumoto, M. Hikosaka, O. (2010). Dopamine in motivational control: rewarding, aversive, and alerting. Neuron, 68, 815-834.
[4] Lang, P. J., Bradley, M. M.& Cuthbert, B. N. (1997). Motivated attention: Affect, activation, and action. In P. J. Lang, R. F. Simons & M. Balaban (Eds.), Attention and orienting (pp. 97–135). Mahwah, NJ: Erlbaum.
[5] Codispoti, M., Ferrari, V. & Bradley, M.M. (2007). Repetition and ERPs: Distinguishing early and late processes in affective picture perception. Journal of Cognitive Neuroscience, 19, 577-586.
[6] Ferrari,V., Codispoti, M., Cardinale, R. & Bradley, M.M. (2008). Directed and Motivated Attention during Processing of Natural Scenes. Journal of Cognitive Neuroscience, 20, 1753-1761.
[7] Bradley, M.M. ( 2009). Natural selective attention: Orienting and emotion. Psychophysiology, 46, 1-11.
[8] Shanks, D.R. (1993). Human instrumental learning: A critical review of data andtheory.British Journal of Clinical Psychologhy,84: 319–354.
[9] Schultz, W. (2006). Behavioral theories and the neurophysiology of reward. Annual Review in Psychology,57, 87-115.
[10] Shanks, D.R. (2007). Associationism and cognition: Human contingency learningat 25. Quarterly Journal of Experimental Psychology, 60, 291–309.
[11] Shanks, D.R. (2010). Learning: From association to cognition. Annual Reviewof Psychology, 61, 273–301.
[12] Castro, L. & Wasserman, E.A. (2010). Animal learning. Wiley Interdisciplinary Reviews - Cognitive Science, 1, 89–98.
[13] Chelazzi, L., Perlato, A., Santandrea, E. & Della Libera, C. (2013). Rewards teach visual selective attention. Vision Research, 85, 58-72.
[14] Della Libera, C., & Chelazzi, L. (2006). Visual selective attention and the effects ofmonetary rewards.Psychological Science, 17, 222–227.
[15] Della Libera, C., & Chelazzi, L. (2009). Learning to attend and to ignore is a matter ofgains and losses.Psychological Science, 20, 778–784.
[16] Anderson, B. A., Laurent, P. A., & Yantis, S. (2011a). Value-driven attentional capture.Proceedings of the National Academy of Sciences of the United States of America,108, 10367–10371.
[17] Anderson, B. A., Laurent, P. A., & Yantis, S. (2011b). Learned value magnifiessalience-based attentional capture.PLoS ONE, 6: e27926.
[18] Eimer, M. (1996). The N2pc component as an indicator of attentional selectivity. Electroencephalography and Clinical Neurophysiology, 99, 225-234.
[19] Woodman, G.F. & Luck, S.J. (2003). Serial deployment of attention during visual search. Journal of experimental psychology. Human perception and performance, 29, 121-138.
PIANO DI FORMAZIONE DELL’ASSEGNISTA
Durante la durata dell'assegno di ricerca, la formazione dell'assegnista comprenderà una serie di attività volte
ad approfondire aspetti legati a :
1. tematiche teoriche
2. metodologie e loro applicazione
3. divulgazione scientifica dei risultati.
Formazione teorica e metodologica
L'approfondimento teorico proposto verterà su temi fondamentali della neurobiologia dell’attenzione
selettiva, ed in particolare:
a) uso di risposte fisiologiche come sonda di processi cognitivi;
b) modulazione attentiva ed emozionale delle risposte psicofisiologiche, sia a livello periferico che
centrale;
c) ruolo dell’apprendimento nell’attenzione
Formazione metodologica
A supporto dello studio degli argomenti teorici trattati, saranno approfonditi i seguenti aspetti metodologici:
a) fasi di elaborazione del biosegnale (con particolare interesse all'analisi delle oscillazioni del tracciato
elettroencefalografico)
b) localizzazione delle fonti del segnale EEG
Divulgazione scientifica dei risultati
I progressi compiuti saranno discussi in periodici incontri interni al gruppo di ricerca e in incontri con
ricercatori di altri laboratori con cui esistono frequenti e documentate collaborazioni. Gli studi saranno
inviati per la valutazione ed eventuale pubblicazione alle principali riviste nell’ambito delle scienze cognitive
e della psicobiologia. Inoltre, i risultati conseguiti saranno presentati a conferenze di livello internazionale,
quali:
1. Meeting of the Society for Psychophysiological Research (
2. The European Conference on Visual Perception (
3. Meeting of the Psychonomic Society (
4. Annual Cognitive Neuroscience Society Meeting (
Esperienze scientifiche
Al fine di approfondire gli argomenti teorici e metodologici proposti, l'assegnista avrà l’opportunità di svolgere periodi di studio presso laboratori e centri di ricerca che si occupano di tematiche affini.