Affective individual differences and startle reflex modulation

Potentiation of startle has been demonstrated in experimentally produced aversive emotional states, and clinical reports suggest that potentiated startle may be associated with fear or anxiety. To test the generalizability of startle potentiation across a variety of emotional states as well as its sensitivity to individual differences in fearfulness, the acoustic startle response of 17 high- and 15 low-fear adult subjects was assessed during fear, anger, joy, sadness, pleasant relaxation, and neutral imagery. Startle responses were larger in all aversive affective states than during pleasant imagery. This effect was enhanced among high fear subjects, although followup testing indicated that other affective individual differences (depression and anger) may also be related to increased potentiation of startle in negative affect. Startle latency was reduced during high- rather than low-arousal imagery but was unaffected by emotional valence.     

Spectral frequency and the modulation of the acoustic startle reflex by background noise

The rat's (Long-Evans) acoustic startle reflex to a high-frequency tone burst (10.5 kHz) was depressed by intense high-frequency band-pass noise (8-16 kHz) but enhanced by low frequency noise (1-2 kHz). However, contrary to the hypothesis that the depression of startle in intense background noise is produced by sensory masking, the reflex to a low-frequency tone burst (at 1 kHz) was depressed by both high- and low-frequency band-pass noise. Two additional hypotheses are offered to supplement sensory masking in order to explain the asymmetry in these data. The first is that the intratympanic reflex, which acts as a high pass filter on acoustic input, is elicited in intense backgrounds. The second is that acoustic startle reflexes elicited by intense low-frequency tones are in part elicited by their high-frequency distortion products and that these distortion products are then masked by high-frequency background noise.     

Emotional-processing in posttraumatic stress disorder II: startle reflex modulation during picture processing

This study examined the impact of a trauma-related stressor on subsequent emotional behavior in veterans with (n = 35) and without (n = 24) posttraumatic stress disorder (PTSD). Self-report and physiological responses, including acoustic startle, were recorded during viewing of emotionally evocative photographs at baseline and following exposure to trauma-related and non-trauma-related stressors. The 2 groups exhibited equivalent patterns of emotional response across self-report and physiological measures at baseline. In contrast, following the trauma challenge, participants with PTSD showed a pattern of startle modulation suggestive of greater defensive reactivity and reduced visual perceptual engagement. These findings, along with augmented corrugator EMG reactivity during the same interval, suggest that trauma-related reexperiencing primes subsequent negative emotional responding in individuals with PTSD.     

Emotion, attention, and the startle reflex

This theoretical model of emotion is based on research using the startle-probe methodology. It explains inconsistencies in probe studies of attention and fear conditioning and provides a new approach to emotional perception, imagery, and memory. Emotions are organized biphasically, as appetitive or aversive (defensive). Reflexes with the same valence as an ongoing emotional state are augmented; mismatched reflexes are inhibited. Thus, the startle response (an aversive reflex) is enhanced during a fear state and is diminished in a pleasant emotional context. This affect-startle effect is not determined by general arousal, simple attention, or probe modality. The effect is found when affects are prompted by pictures or memory images, changes appropriately with aversive conditioning, and may be dependent on right-hemisphere processing. Implications for clinical, neurophysiological, and basic research in emotion are outlined.     

The fear potentiated startle effect. Blink reflex modulation as a result of classical aversive conditioning

A differential conditioning study examined whether an acoustic startle probe, presented during extinction of an aversively conditioned visual stimulus, potentiated the reflex eyeblink response in humans and whether this potentiation varied with the change in affective valence of the conditioned stimulus. Sixty college students were randomly assigned to view a series of two slides, depicting either unpleasant/highly arousing, unpleasant/moderate arousing, neutral/calm, pleasant/moderate arousing or pleasant/highly arousing scenes and objects (duration: 8 sec). During preconditioning (8 trials) and extinction (24 trials) acoustic startle probes (white noise bursts [50 ms; 95 dBA] were administered during and between slide presentation). During acquisition (16 trials) CS+ was reinforced by an electric shock. Startle response magnitudes significantly increased from preconditioning to extinction and were substantially larger to CS+. Conditioned startle reflex augmentation linearly increased with the pleasantness of the slides. Furthermore, subjects showed a greater post-conditioning increase of judged aversiveness to slides that they had previously reported to be more pleasant, exactly paralleling the startle reflex results.     

Directed attention influences the modification of startle reflex probability

The present study was designed to investigate the effect of directed attention on elicitation and modification of the startle reflex. 30 adult human subjects received 90 dB(A) broadband noise startle stimuli either alone or preceded by a 60 dB(A) prepulse (either 2000-Hz tone, 1000-Hz tone, or broadband noise). Subjects were instructed to attend to one of the three prepulses during half the trials and to ignore all stimuli during the rest of the trials. The probability of responding while attending to a prepulse was significantly lower than the probability of responding while ignoring the prepulses. Responding to the prepulses was also more probable while subjects were attending to the prepulses, and these effects were more pronounced for tone than for noise prepulses. These results suggest that directed attention can influence the probability of the startle reflex without influencing startle amplitude or latency.     

Sensitization and aversive conditioning: Effects on the startle reflex and electrodermal responding

Animal data suggest that shock sensitization as well as aversive learning potentiates the acoustic startle reflex. The present experiment tested, whether this shock sensitization also occurs in human subjects and whether it precedes aversive conditioning. Sixty subjects viewed—prior to conditioning—a series of slides of different emotional contents including the to be conditioned stimuli (CSs). Afterwards, the experimenter attached the shock electrodes and initiated shock exposure. Then, subjects were randomly assigned to view a series of two slides, each for eight acquisition trials in which one slide was followed by a shock. Subsequently, extinction trials (12 for each slide) were administered. During preconditioning, acquisition, and extinction, startle probes occurred unpredictably during and between slide viewing. Preconditioning data replicated previous results by Lang and his associates, showing that the startle response magnitude is directly related to the affective valence induced by the slides. Shock exposure strongly facilitated the startle reflex magnitude. This shock sensitization was absent for the skin conductance response. Course of learning also varied for both response systems. The data suggest that startle reflex potentiation indexes the acquisition of an avoidance disposition, which is preceded by a general sensitization of the protective reflexes. Skin conductance learning follows arousal changes and is modulated by cognitive processes.     

Modulation of the acoustic startle reflex in humans in the absence of anticipatory changes in the middle ear reflex

If a weak tone precedes an intense tone, then the acoustic startle eyeblink reflex elicited by the stronger stimulus is inhibited. It has been suggested that the leading stimulus gives rise to a protective middle ear reflex that attenuates the effective intensity of the second. This hypothesis was tested and disproved. In seven subjects intense tone bursts sufficient to elicit both intratympanic and eyeblink responses were presented sometimes alone and sometimes preceded at various lead times (25 to 400 msec) by a weak tone. The weak tone inhibited the amplitude of the eye blink to the strong tone, maximally at intervals of 100 to 200 msec, but was never seen to produce any of the anticipatory impedance changes that would be characteristic of middle ear reflex activity during the interval between the two stimuli.     

Age-related affective modulation of the startle eyeblink response: older adults startle most when viewing positive pictures

Previous studies reveal age by valence interactions in attention and memory, such that older adults focus relatively more on positive and relatively less on negative stimuli than younger adults. In the current study, eyeblink startle response was used to measure differences in emotional reactivity to images that were equally arousing to both age groups. Viewing positive and negative pictures from the International Affective Picture System had opposite effects on startle modulation for older and younger adults. Younger adults showed the typical startle blink pattern, with potentiated startle when viewing negative pictures compared to positive pictures. Older adults, on the other hand, showed the opposite pattern, with potentiated startle when viewing positive pictures compared to viewing negative and neutral pictures. Potential underlying mechanisms for this interaction are evaluated. This pattern suggests that, compared with younger adults, older adults are more likely to spontaneously suppress responses to negative stimuli and process positive stimuli more deeply.     

Development of selective attention in young infants: Enhancement and attenuation of startle reflex by attention

This study examined the effect of level of attention engagement on the modification of the blink reflex in young infants. Infants at 8, 14, 20, or 26 weeks of age were presented with interesting visual or auditory stimuli. At delays defined by changes in heart rate known to be associated with sustained attention or attention disengagement, blink reflexes were elicited by visual or auditory blink reflex stimuli. Blink amplitude varied according to the level of attention, and the match between the foreground and blink reflex stimulus. If the infant was attending to the foreground stimulus, a blink reflex stimulus in the same modality resulted in enhanced blink reflex magnitude. A blink reflex stimulus in the other modality resulted in an attenuated blink reflex magnitude. If attention was not engaged with the foreground stimulus, this modulation of the blink reflex did not occur. This ‘selective modality effect’ showed an increasing tendency to occur between 8 and 26 weeks of age. These results show that selective attention to modalities increases over this age range.     

Gender of the expresser moderates the effect of emotional faces on the startle reflex

It has been suggested that the impact of emotional expressions on the startle reflex is influenced by the intention communicated by the expression (e.g., the intention to attack). However, we propose that the meaning of an emotional expression is not only based on the intention, but is also influenced by characteristics of the expresser such as gender: since men are typically seen as more dominant than women, anger expressed by men should be perceived as particularly threatening, thus amplifying the startle response. We compared the influence of anger, fear and neutral expressions shown by men and women on the startle reaction. Startle reactions were measured using electromyography. As predicted, we found stronger startle reactions after the presentation of anger expressed by men compared to fearful and neutral expressions shown by men. For female expressers, the startle response was not affected by expression type.     

The chronometry of affective startle modulation in unipolar depression

Affective startle eyeblink modulation by unipolar depressed and nondepressed participants was assessed during the anticipation and viewing of emotional pictures. Anticipatory startle probes were presented at 2,000 ms and 750 ms before picture onset. Startle probes during picture viewing were presented at 300 ms and 3,500-4,500 ms after picture onset. Although nondepressed participants demonstrated the predicted quadratic and linear patterns of responding in the 2,000-ms anticipatory and 3,500-4,500-ms viewing conditions, respectively, depressed participants were not significantly responsive to differences among picture valence categories at these probe conditions. There were no between-groups differences in startle modulation at the other two probe intervals, in picture ratings, or in behavioral responses to pictures. There was also little evidence of hyperresponsivity to negatively valenced stimuli in the depressed group. These results indicate that depression-related affective hyporesponsivity extended to startle modulation but that the nature and magnitude of the differences between depressed and nondepressed individuals were conditional on the specific cognitive and motivational processes recruited at different points in time.     

Affective ratings and startle modulation in people with nonclinical depression

This study tested predictions based on the emotion context insensitivity (ECI) hypothesis of Rottenberg, Gross, and Gotlib (2005) that a nonclinical sample of people with depressive symptoms would show reduced responses to both positive and negative stimuli relative to people without depression and would show an enhanced response to novelty. Seventy individuals completed diagnostic questionnaires, made ratings of 21 affectively valenced pictures, and then viewed the same 21 pictures and 21 novel pictures while startle blink responses were recorded from electromyographic activity of the orbicularis oculi. People with scores on the Beck Depression Inventory (BDI; Beck, Ward, Mendelson, Mock, & Erbaugh, 1961) indicative of depression demonstrated a lack of affective startle modulation compared to the nondepression group. For all participants, the startle response was larger for novel pictures than for previously viewed pictures, but scores on the BDI were not related to response to novelty. Taken together, the results suggest that nonclinical depression is associated with a lack of affective modulation of startle, as has been shown for clinical depression.