Maciokas JB, Britten KH. Extrastriate area MST and parietal area VIP similarly represent forward headings. J Neurophysiol 104: 239 -247, 2010. First published April 28, 2010 doi:10.1152/jn.01083.2009. Many studies have documented the involvement of medial superior temporal extrastriate area (MST) in the perception of heading based on optic flow information. Furthermore, both heading perception and the responses of MST neurons are relatively stable in the presence of eye movements that distort the retinal flow information on which perception is based. Area VIP in the posterior parietal cortex also contains a robust representation of optic flow cues for heading. However, the studies in the two areas were frequently conducted using different stimuli, making quantitative comparison difficult. To remedy this, we studied MST using a family of random dot heading stimuli that we have previously used in the study of VIP. These stimuli simulate observer translation through a three-dimensional cloud of points, and a range of forward headings was presented both with and without horizontal smooth pursuit eye movements. We found that MST neurons, like VIP neurons, respond robustly to these stimuli and partially compensate for the presence of pursuit. Quantitative comparison of the responses revealed no substantial difference between the heading responses of MST and VIP neurons or in their degree of pursuit tolerance. I N T R O D U C T I O NThe medial superior temporal area of macaque extrastriate cortex (MST) is perfectly suited for the analysis and representation of the wide-field image motions that arise from observer motion through the environment. Neurons in MST have large receptive fields (RFs) selective for different components of optic flow present in such scenes (Duffy and Wurtz 1991;Graziano et al. 1994;Tanaka et al. 1986). Additionally, they are tuned for the direction of visually simulated trajectories in a variety of visual environments (Gu et al. 2006;Page and Duffy 2003;Paolini et al. 2000). Last, MST cells explicitly represent the direction of ongoing smooth pursuit eye movements (Komatsu and Wurtz 1988).The direct involvement of MST neurons in heading perception has been suggested by several experiments. First, MST neurons are sufficient for the discrimination of heading based on either visual or vestibular cues ) in a two-alternative task. Second, in this task, their responses covary with perceptual decisions on a trial-by-trial basis ). Most importantly, electrical microstimulation biases perceptual judgments of heading in a two-alternative task (Britten 1996).The ventral intraparietal area (VIP) in the posterior parietal cortex is functionally distinct from MST in many ways. It is a multimodal area, showing visual Colby et al. 1993;Schaafsma and Duysens 1996), vestibular (Schlack et al. 2002), somatosensory (Duhamel et al. 1998;Schlack et al. 2005), auditory (Schlack et al. 2005), and smooth pursuitrelated responses (Schlack et al. 2003). Visual responses in VIP are often direction selective (Colby et al. ...

The attentional blink (AB) is a marked deficit in detecting a second target for up to 600 ms within a rapid serial visual presentation (RSVP). The phenomenon of the AB has typically been investigated using college students between 18 and 25 years of age. However, the AB has not been closely studied within a senior population. Past studies have found age-related attentional deficits using cued location, visual conjunction search, and divided-attention tasks, all spatial measures of attention; however, the physiological basis of these deficits is not fully understood. The role of cognitive slowing and reduced attentional resources was examined using the AB paradigm--a temporal measure of attention. Experiment 1 found an age-related deficit independent of lag for the single-task condition and a larger more prolonged deficit for dual-task conditions. Experiment 2, using similar methods to Experiment 1, incorporated a more rigorous cognitive screen. A similar deficit was found for the dual-task condition. However, single-task trials appeared to involuntarily capture attentional resources for the older population. Comparisons revealed a significant difference in the magnitude and the time course of the AB with age. Results are discussed in the context of cognitive slowing and reduced attentional resources.

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