The dorsal and ventral visual stream dichotomy has been the subject of immense amounts of research and yet remains an area of some controversy. The ventral stream is well understood to be essential for visual perception, and object processing. The dorsal stream, however, appears more difficult to pin down. Recent models of visual processing have highlighted the role of the dorsal stream in driving bottom-up attention networks to facilitate later detailed object processing in the ventral stream. We sought to investigate the timing of necessary processing in the lateral occipital cortex (LO) in the ventral stream, extrastriate dorsal stream area V5, and the temporoparietal junction (TPJ) - a parietal area suggested to be involved in salience detection within a ventral parieto-frontal attention network, and a potential candidate for the termination point of the dorsal stream. Transcranial Magnetic Stimulation (TMS) was used to target either LO, V5, or TPJ at three latencies following visual target onset, using paired pulses with 25 ms inter-pulse intervals (providing a total range of 66 a?? 200 ms). Participants completed an object recognition task with two conditions: Abrupt contrast onset/offset, which was expected to tap into dorsal stream attention networks, or alternatively ramped contrast onset/offset, which was not expected to be well-suited to activating bottom-up attention networks. Whilst LO and TPJ showed a differential critical involvement for abrupt onset objects, interestingly all cortical sites showed a later critical involvement for the reduced-transience ramped onset stimuli. The temporal profile of these target sites are discussed in terms of recent models of visual processing.
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