1. Attention to Orientation Results in an Inhibitory Surround in Orientation Space Acknowledgements Funding for this project was provided to MT through a CIHR Vision Health Research Grant and an NSERC Post-Doctoral Fellowship; and to JT through a Canada Research Chair in Computational Vision. References Cutzu. F., & Tsotsos, J. (2003). The selective tuning model of attention: psychological evidence for a suppressive annulus around an attended item. Vision Research, 43, 205 - 219. Luck, S., Chelazzi, L., Hillyard, S., & Desimone, R. (1997). Neural mechanisms of spatial selective attention in areas V1, V2, and V4 of macaque visual cortex. Journal of Neurophysiology, 77, 24 - 42. O’Connor D., Fukui, M., Pinsk, M. & Kastner, S. (2002). Attention modulates responses in the human lateral geniculate nucleus. Nature Neuroscience, 5, 1203 – 1209. Tsotsos J., Culhane, S., Wqai, W., Davis, N., & Nuflo, F. (1995). Modeling visual attention via selective tuning. Artificial Intelligence, 78, 507 - 547. Introduction It is computationally impossible for the visual system to fully process all of the visual information that arrives at the eye. In order to get around this limitation, a mechanism that selects regions of interest for additional processing is required. This mechanism is commonly referred to as visual attention. Attention can be guided by bottom-up factors, such as stimulus saliency, as well as top-down factors, such as cueing. The purpose of this experiment is to test a key prediction of one such model: the Selective Tuning model (Tsotsos et al., 1995). The Selective Tuning (ST) Model Posits an annulus of inhibition around attended objects that gradually dissipates as the distance from the attended object increases. This inhibitory surround is predicted to occur in the spatial domain, as well as in other non-spatial feature domains. In the current experiment subjects are presented striped disks made up of either straight or jagged stripes. Trial Trial Sequence Experimental Logic According to the ST model, orientations near an attended orientation will be inhibited, while more distant orientations will not. In the spatial domain the ST model predicts better performance for stimuli presented far from the attended location than for stimuli presented near the attended location. This prediction has been confirmed in behavioural studies (Cutzu & Tsotsos, 2003) as well as neurophysiological studies (e.g., Luck et al., 1997). As in the spatial domain, the ST model also predicts an inhibitory surround in other object dimensions. The present experiment aims to test this prediction in the orientation domain. The Experimental Design Eight blocks of 100 trials Seventy trials at a to-be-attended orientation and 10 trials at each other orientation/block Each orientation was the to-be-attended orientation twice per experiment Before each block, subjects were informed of, and instructed to attend to the to-be-attended orientation. A points system was employed whereby subjects received points for correct responses and lost points for incorrect responses. Points values were doubled for trials at the attended orientation. These measures were taken to focus attention at the to-be-attended orientation. Conclusions The results of this experiment indicate that attending to a point in orientation space facilitates performance at that orientation, while inhibiting nearby orientations, but not more distant ones. This result is in agreement with the prediction of the Selective Tuning model of an annulus of inhibition around attended objects in both spatial and non-spatial domains, such as orientation. fMRI results (O’Connor et al., 2003) indicate that in the spatial domain, attentional modulation enhances processing at the attended location as well as inhibits processing at unattended locations. Our results demonstrate a similar pattern of behavioural results in the orientation domain, suggesting that attention modulates processing in a similar manner in both domains. Baseline activity Inhibitory Surround Baseline activity The Task: To indicate whether the stripes are straight or jagged. On half of the trials the stripes are straight. From trial to trial the orientation of the stripes varies. Four orientations were employed: 22°, 67°, 122°, and 157°. For each orientation, two orientations are near (45° CW, CCW) and one is far (90°). Straight Jagged Attended Orientation Near Orientations Far Orientation Each trial began with the fixation marker, which remained on screen until the subject pressed the spacebar. All stimuli subtended 5º of visual angle (width and height) and were presented on a grey background. 250 ms after the subject pressed the spacebar, fixation was replaced with a pre-stimulus mask for 83 ms. The stimulus was then displayed for a duration dependent on the subject and designed to keep performance around 80%. This value varied from 67 to 150 ms. The stimulus was then replaced by a post-stimulus mask for 83 ms after which the screen went grey until the subject made a response. Attentional Pass Zone According to the ST model, performance should be best at the attended orientation followed by the far orientation and finally the near orientations. AttendedNearFar Proportion Correct Michael Tombu & John Tsotsos, Centre for Vision Research, York University Results (N=8) The attentional effect (Attended - Unattended near) was 7.4% and the inhibition effect (Unattended Far - Unattended Near) was 4.0%. One subject showed no attentional or inhibition effects. For the remaining seven subjects, attentional effects ranged from 4.1 to 12.0% and inhibition effects ranged from 3.3 to 5.5%.