The role of reentrant processes in feature binding: Evidence from neuropsychology and TMS on late onset illusory conjunctions

Abstract

We report data on illusory conjunctions (ICs) in a colour/letter identification task from a patient with simultanagnosia following bilateral parietal lesions and from a study using transcranial magnetic stimulation (TMS) with normal participants. We show that, even though target conjunctions were reported well above chance across a range of exposure durations, ICs were only generated at longer display exposures while feature errors decreased across time. With normal participants we found that TMS to the right posterior parietal cortex but not to occipital cortex increased the number of ICs. Moreover, ICs tended to occur after delayed stimulation, with the critical time window for stimulation being later for ICs than for feature errors. The data provide support for the critical role of posterior parietal cortex in a late process of feature binding.

Keywords:

• Attention
• Illusory conjunction
• Transcranial magnetic stimulation
• Parietal cortex

Acknowledgements

This work was supported by grants from the BBSRC and MRC (UK).

Notes

¹In offline TMS a train of pulses is delivered to the region of interest at the start of the experiment, prior to a task being performed, with the aim being to affect cortical excitability for the duration of the task.

²The scores for the percentage of conjunction errors here differ from those in Figure 4. The data in Table 1 show conjunction errors as a proportion of the total errors generated, needed to test performance relative to chance. Figure 4 shows conjunction errors as a percentage of the total numbers of trials in the experiment, to give an indication of errors relative to overall performance.