Cortical Contributions to Saccadic Suppression

The stability of visual perception is partly maintained by saccadic suppression: the selective reduction of visual sensitivity that accompanies rapid eye movements. The neural mechanisms responsible for this reduced perisaccadic visibility remain unknown, but the Lateral Geniculate Nucleus (LGN) has been proposed as a likely site. Our data show, however, that the saccadic suppression of a target flashed in the right visual hemifield increased with an increase in background luminance in the left visual hemifield. Because each LGN only receives retinal input from a single hemifield, this hemifield interaction cannot be explained solely on the basis of neural mechanisms operating in the LGN. Instead, this suggests that saccadic suppression must involve processing in higher level cortical areas that have access to a considerable part of the ipsilateral hemifield

Transcranial magnetic stimulation of medial-frontal cortex impairs the processing of angry facial expressions.

Growing evidence suggests that the recognition of different emotional states involves at least partly separable neural circuits. Here we assessed the discrimination of both anger and happiness in healthy subjects receiving transcranial magnetic stimulation (TMS) over the medial-frontal cortex or over a control site (mid-line parietal cortex). We found that TMS over the medial-frontal cortex impairs the processing of angry, but not happy, facial expressions of emotion

Chronostasis without voluntary action.

In a previous study we explored auditory chronostasis and suggested an arousal account of this temporal illusion rather than one dependent on backdating actions to the onset of a motor event. Here we present three experiments designed to distinguish between two competing accounts of the mechanisms underlying the illusion. Experiment 1 investigated whether voluntary movements are necessary for the illusion to occur. Experiment 2 sought to clarify whether auditory chronostasis occurs when the intervals to be judged are continuous (temporally contiguous) rather than separate events. Experiment 3 was designed to establish whether increased task demands account for the illusion. Together the results from these experiments show that chronostasis is an illusion that is not dependent on voluntary action, can occur without a change in the spatial location of the stimulus (thus precluding an account based on spatial attention), occurs with discrete as well as continuous events, and is affected by the salience of the termination of the event to be timed rather than the onset. Collectively these findings suggest that the mechanisms underlying chronostasis are best explained by an arousal hypothesis since neither attention nor backdating to action can account for the commonalities between chronostasis in the auditory, visual and tactile domains

Auditory chronostasis: hanging on the telephone.

The perception of time can be illusory: we have all waited anxiously for important seconds to tick away slowly at the end of a football game and have experienced the truth of the adage "time flies when you're having fun." One illusion of time experience that has recently been investigated, the apparent slowing of the movement of the second hand on the clock when one first looks at it, has been termed "chronostasis," and it has been suggested that the effect is unique to vision and is dependent on eye movements. We sought to test whether the effect is really unique to vision or whether it can also be produced with auditory stimuli. Subjects were asked to judge the length of a silent gap between two tones presented through headphones. When the tones were presented to one ear, subjects judged the duration of the gap veridically. When subjects were required to shift concentration from one ear to the other, however, the judgement of time showed that the auditory system is also susceptible to chronostasis. We suggest that this generalization of chronostasis to another sensory system is consistent with theories of time perception that emphasize a single, multimodal clock for duration estimation rather than a mechanism that is dependent on motor acts