Conversation effects on neural mechanisms underlying reaction time to visual events while viewing a driving scene using MEG

Abstract

Magnetoencephalography (MEG) imaging examined the neural mechanisms that modulate reaction times to visual events while viewing a driving video, with and without a conversation. Twenty-four subjects ages 18-65 were monitored by whole-head MEG. The primary tasks were to monitor a driving video and to depress a foot pedal in response to a small red light presented to the left or below the driving scene at unpredictable times. The behavioral reaction time (RT) to the lights was recorded. The secondary task was a hands-free conversation. The subject pressed a button to answer a ring tone, and then covertly answered pre-recorded non-emotional questions such as "What is your birth date?" RTs for the conversation task (1043 ms, SE=65 ms) were slightly longer than for the primary task (baseline no conversation (944 ms, SE=48 ms)). During the primary task RTs were inversely related to the amount of brain activity detected by MEG in the right superior parietal lobe (Brodmann's Area 7). Brain activity was seen in the 200 to 300 ms range after the onset of the red light and in the visual cortex (BA 19) about 85 ms after the red light. Conversation reduced the strengths of these regression relationships and increased mean RT. Conversation may contribute to increased reaction times by (1) damping brain activation in specific regions during specific time windows, or (2) reducing facilitation from attention inputs into those areas or (3) increasing temporal variability of the neural response to visual events. These laboratory findings should not be interpreted as indicative of real-world driving, without on-road validation, and comparison to other in-vehicle tasks.

Figure 1

Video display of the driving scene with small red dot stimulus in the lower central viewing area and in the left peripheral area.

Figure 2

This Graph displays the reaction times (milliseconds) for the no conversation condition (black) compared to the conversation condition (white) Behavioral lab (467 ± 12 ms v. 508 ± 20ms respectively) and in the MEG lab (945 ms ± 48ms v. 1043 ± 65 ms respectively). Note longer reaction times occur during the conversation condition in both environments.

Figure 3

The waveforms display the filtered MEG data for one second after the red light stimulus appeared. (t=0) in both conditions for one subject. The four waveforms represent the different RT. Divided in to separate bins based on reaction time seen as the left of the wave form. Red line indicates the evoked response that correlated with reaction time.

Figure 4

The regression line is fit to the amplitude of MEG data projected on the RT related component. Thus, the vertical scale specifies the amount of the RT component that must be added to the mean MEG data component to obtain MEG data corresponding to a specific reaction (horizontal scale). The RT component shown is MEG data from the conversation condition for one subject (shown on the right). The RT component for the no conversation condition is similar but not identical. Further, both RT and mean response components differ across individuals.

Figure 5

Neural correlate in Right Parietal Region related to event detection during the primary condition (No Conversation) only. This MEG/MRI image represents the group average of brain activation from 19 subjects. Red Arrow indicates changes taking place in the right partial region. Each line in the Graph in the upper right hand corner represents a different response time. Red line indicates the latency of the MEG/MRI image. Amplitude scale is in percent change.

Figure 6

Neural correlate in right parietal region related to event detection during the primary condition plus secondary task (Conversation). This image represents a group average of brain activation from 19 subjects. Red Arrow indicates NO changes are taking place in the right partial region. Red Arrow indicates changes taking place in the right partial region. Each line in the Graph in the upper right hand corner represents a different response time. The red line in this graph marks the time point corresponding to the brain images on the left. Amplitude scale is in percent change.

Figure 7

A) Brain responses at 200ms during primary task (response to lights while viewing driving video). B) Brain responses to primary plus secondary task (conversation) at 200ms. The strength of the regression relationship between the brain activity and reaction time at this particular time interval is decreased in the conversation condition (B), in the right superior parietal lobe.

Figure 8

A) Average cortical changes in the occipital brain region at 80 ms after onset of red dot during the primary condition (response to lights while viewing driving video). B) Average cortical changes in the occipital brain region during the primary condition plus the secondary tasks of conversation. The strength of the regression relationship between the brain activity and reaction time at this particular time interval is decreased in the conversation condition (B), in the visual occipital cortex.