A startling absence of emotion effects: Active attention to the startle probe as a motor task cue appears to eliminate modulation of the startle reflex by valence and arousal
Highlights
► Previous startle-affective imagery research had asked participants to ignore the startle probe, while in this study the probe is a significant cue. ► When the startle probe signals an RT task, affective valence and arousal no longer modulate the startle reflex. ► An active, rather than defensive response set and/or a required motor response to the startle probe may interfere with affective startle modulation.
Introduction
The startle reflex, the involuntary response to a sudden onset stimulus, has received much research interest among psychophysiologists because it can serve as a probe into both affective and cognitive processes (Dawson et al., 1999). The magnitude and latency of the startle response are modulated by factors including affective valence (Vrana et al., 1988) and arousal (Witvliet and Vrana, 1995, Witvliet and Vrana, 2000), presence of a non-startling prepulse (Blumenthal, 1999, Robinson and Vrana, 2000), direction of attention toward the startle probe modality (Anthony and Graham, 1985), or engagement in an effortful mental task (Panayiotou and Vrana, 1998). The valence effect on startle (potentiated startle during negative emotion) is extremely robust. It has been replicated dozens if not hundreds of times and has been obtained with a range of different affective manipulations such as picture viewing (e.g., Bradley et al., 1996a, Sloan and Sandt, 2010, Vrana et al., 1988), imagery (e.g., McTeague et al., 2010, Witvliet and Vrana, 1995, Witvliet and Vrana, 2000), and olfactory stimuli (Miltner et al., 1994). Within the imagery paradigm valence and arousal appear to modulate startle independently: negative emotions, such as fear and sadness, result in larger startle blink responses than positive emotions such as joy or pleasant relaxation, and high arousal emotions, such as joy or fear, result in larger startle blink responses compared to less arousing emotions such as pleasant relaxation or sadness (Cook et al., 1991, Robinson and Vrana, 2000, Witvliet and Vrana, 1995, Witvliet and Vrana, 2000).
Attention also modulates the startle response independently of affect. The effect of attention on the startle has been demonstrated in studies that show that when attention is directed to the sensory modality that contains the startle evoking stimulus the reflex is potentiated (Anthony and Graham, 1985). Performing a reaction time (RT) response to an imperative stimulus that occurs simultaneously with the startle probe enhances the startle reflex (Valls-Solé et al., 1995, Lipp et al., 2006) and reduces startle habituation (Valls-Solé et al., 1997), an effect known as the StartReact effect (Valls-Solé et al., 2005). An explanation for this effect has been the summation of the startle reflex and a pre-programmed movement to the imperative task requiring the RT motor response (Siegmund et al., 2001). Conversely, startle is attenuated if attention is directed to a different modality than the startle probe (Schicatano and Blumenthal, 1997), particularly when the task to be completed in this modality is complex (Neumann, 2002). However, this reduction in startle response during cross-modal monitoring has not been consistently found, as Lipp (2002) reported that attending to a significant task-relevant stimulus, even if it is in a different modality than the startle probe, enhances the startle response compared to a task-irrelevant condition (Lipp and Hardwick, 2003). Such cross-modal facilitation is not unequivocal either, however, as it was not obtained for startle magnitude, while it was present for startle latency in some studies (e.g., Lipp et al., 2000).
In addition to being modulated by task-relevant stimuli, the startle reflex is enhanced during effortful mental tasks. For instance, startle responses are larger during active imagery, a task that requires cognitive effort, compared to periods when participants engage in a less effortful cognitive task (Robinson and Vrana, 2000), and responses are larger when participants rehearse digits compared to passively listening to digit presentation, especially when the digit rehearsal is more effortful (Panayiotou and Vrana, 1998).
Although attentional and emotional processes often interact, usually research on the affective modulation of the startle response does not simultaneously examine sensory and cognitive variables that may be influencing the response “except as alternative explanations of the emotion effects” (Hawk and Cook, 2000, p. 5). In fact, the experimental paradigm within which affective startle modulation has typically been studied entails instructions to participants to focus attention on the emotion induction task and ignore the startle probe (e.g., Codispoti et al., 2001). In the prepulse paradigm, the interaction of affective and attentional processes is most clearly seen. When the prepulse stimulus, which precedes and overlaps with the startle probe, is an emotional picture or imagery, studies show that the attention-engaging properties of the prepulse interact with its emotional aspects (e.g., Filion et al., 1993). However, when the prepulse stimulus is not the emotional stimulus, the prepulse and emotion modulate the startle response independently (Hawk and Cook, 2000, Robinson and Vrana, 2000).
Few studies have examined the effects of attending to the startle probe itself on affective modulation, but most find that manipulating the task-relevance of the startle probe does not impair affective startle modulation. Extant studies relied on the affective picture paradigm. For example, Cuthbert et al. (1998) found that startle modulation by affective pictures did not vary as a function of whether the startle probe was attended to. From this they concluded that emotional responding is automatic and obligatory, and is independent of the attentional aspects of the probe and its signal value. Haerich (1994) found that, regardless of whether or not participants attended to the startle probe to judge its duration, negative emotion primarily modulated startle. Negative emotion was triggered by instructions that made the startle probe an aversive stimulus, and no active response to the probe was required. Bradley et al. (1996b) found that making a startle probe significant by requiring a simple RT in response to its occurrence did not affect modulation of the startle by concurrent viewing of affective pictures. Thus, so far, in all cases affective modulation of the startle is found even when the startle probe is task-relevant. No data exist, however, on startle modulation during affective imagery when the probe is task-relevant.
Lang's explanation for startle enhancement by negative valence is that affective “matching” occurs between the defensive reaction evoked by the startle probe and the negative affective foreground (Lang, 1995). Thus, both the startle probe and a negative affective context call for the participant to withdraw or take a defensive, stance enhancing the startle response. In the studies described above, where the startle probe was task-relevant, and particularly when one had to perform an RT response to it, it can be argued that the startle stimulus acquires an “approach” rather than “avoidance” meaning. Apparently, within the picture paradigm this did not over-ride the robust effect of the emotional foreground on startle, but this effect has not been studied in the imagery paradigm. Picture viewing, a situation that directs attention to interesting visual stimuli that may more easily sustain attention, is very different from imagery, where mental processing rather than sensory attention is required, and where it may be harder to sustain attention.
The primary aim of this research was to examine emotional valence and arousal modulation of the acoustic startle response during affective imagery while participants attend to the acoustic startle probe stimulus for the purposes of a reaction time (RT) task to the stimulus itself. The question we sought to answer is whether changing the meaning of the startle stimulus from avoidance to approach (task relevance) would counter its match with the negative affective context produced by the imagery task and consequently reduce affective startle modulation. To examine whether affective modulation of the task-relevant probe differs from the typical affect modulation study, we conducted meta-analytic comparisons with a similar study (Witvliet and Vrana, 1995) that used the same affective materials but in which the startle probe was task irrelevant. It is hypothesized that the standard affective startle modulation effects will be found in the current study; that is, affective valence and arousal will both modulate startle magnitude, and that meta-analytic comparisons between effects in this study and Witvliet and Vrana (1995) will verify the similarity of the results. Further, the startle response should be enhanced during the effortful imagery task compared to a non-effortful baseline task. Heart rate, which increases during arousing imagery (Witvliet and Vrana, 1995, Witvliet and Vrana, 2000), and emotional ratings were collected to provide additional measures of emotional processing during imagery.
Section snippets
Participants
Participants were 27 male and 26 female undergraduate students at a U.S. university who took part in this experiment in return for course credit.
Procedure
Participants completed six blocks of an emotional imagery task, using the same procedure and standardized imagery scripts as Witvliet and Vrana, 1995, Witvliet and Vrana, 2000. At the beginning of each block the participant was given two index cards, each with a sentence-long script describing a scenario representing one of the four emotions. The
Experiment 2
Because it is highly unusual not to find affective modulation of the startle, the present results require replication. Thus a second experiment was conducted with the same procedure but a different set of affective stimuli to further investigate startle modulation when the probe is attended to and significant for an RT task. Experiment 2 added a second emotional content to the negatively valent, high-arousal quadrant, which is the most potent facilitator of the startle reflex (Lang, 1995).
General discussion
Two experiments examined the effects of attending and responding to the startle probe on affective modulation of the startle reflex. The two current experiments found no valence or arousal effect on modulation of the startle reflex response. This is contrary to at least 14 published studies of emotional imagery modulation of the startle response (Cook et al., 1991, Cuthbert et al., 2003, Gautier and Cook, 1997, Hawk et al., 1992, McTeague et al., 2009, McTeague et al., 2010, Miller et al., 2002
Acknowledgements
This research was supported in part by NIH research grant MH46861 awarded to Scott Vrana. The authors would like to acknowledge the assistance of James Cogbill, Jennifer Copp, Jennifer Craig, John Kettler, Katy Koonz, Natalie Milbrandt, Leah O’Connell, Christopher Reid, Uri Weinberg, and David Whittinghill in collecting and reducing these data.
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