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Social Attention to Infants

Table 3. Mean pleasantness and arousal ratings (61 standard error) as a function of target age, target race, and participant race in the pilot study; possible range = 0 to 100.

Pleasantness

Arousal

Infant faces

Adult faces

P-value (infant versus adult)

Infant faces

Adult faces

P-value (infant versus adult)

81.2

77.1

67.4

83.5

(0.7)

(0.9)

(0.7)

(0.9)

35.3

28.3

35.4

42.0

(3.3)

(2.4)

(3.3)

(2.4)

0.001

0.001

0.001

0.001

69.6

78.2

(1.1)

(1.5)

42.8

24.6

(2.8)

(2.1)

0.001

0.001

79.3

84.2

(1.1)

(1.5)

18.3

28.0

(2.8)

(2.1)

0.001

0.001

White Distractors

South Asian Participants

White Participants

South Asian Distractors

White Distractors

South Asian Distractors

Note. The P value refers to a t-test comparing the infant and adult faces per column condition (e.g., comparing ratings of South Asian adult and infant faces by South Asian participants). doi:10.1371/journal.pone.0012509.t003

race: South Asian, White) 62 (participant race: South Asian, White) mixed design, with probe location age and race as within- participants factors.

Apparatus and Stimuli

The task was performed on an IBM-compatible PC using a Philips 19’’ CRT monitor. Stimulus presentation and response collection were managed with E-Prime v1.20 (Psychology Software Tools, Pittsburgh, USA; www.pstnet.com/eprime).The stimuli comprised a probe shape and face images. The probe shape was a small equilateral triangle of RGB value (160, 160, 160) subtending 0.8 cm. Face images, downloaded from the internet, were grayscale portrait images of South Asian and White infants and middle-aged adults (eight in each Age x Race category), all showing neutral to slightly positive facial expressions. The adult stimulus category comprised four female and four male faces. The images were formatted to be similar in terms of contrast, sharpness, brightness, and any salient features. The images were 6 cm 66 cm in size and were presented at 12 cm to the left or right of the fixation cross, giving a visual angle of at 70 cm distance from the screen.

For the experimental task, the faces images were presented in pairs. Each pair comprised an infant face and an adult face of the same race; that is, South Asian infant faces were paired with South Asian adult faces and White infant faces were paired with White adult faces. Assignment of infant and adult faces to the left and right sides of the display was counterbalanced across trials. Note that there were differences between the infant and adult face stimuli other than the presence/absence of kindenschema. In particular, there were clear clothing and hairline cues in the adult faces that were not present in the infant faces. Nonetheless, these differences cannot account for the pattern of findings whereby attentional prioritization of infant over adult faces occurred for own- but not other-race faces, as the same age confound was present in both South Asian and White face stimuli.

Procedure Prior to participation, participants completed consent forms and a personal information sheet on which they indicated their ethnic

origin. They then completed a probe-discrimination task. At the start of each trial, a fixation cross appeared in the centre of the screen for 500 ms. Next, two faces images appeared for 200 ms, one on each side of the fixation cross. After a 50-ms interval, a small triangle appeared for 100 ms at the centre of one of the previous image locations, followed by a blank screen until the participant’s response. Participants indicated whether the probe triangle pointed upwards or downwards by pressing the respective ‘‘J’’ and ‘‘N’’ keys on the computer keyboard. Once a response was recorded, the next trial began. Following a set of 32 practice trials designed to familiarize participants with the task, participants completed 2 blocks of 128 fully randomized trials, giving 64 trials per experimental condition. Upon completion of the task, participants were thanked and informed about the purpose of the experiment.

Statistical Analysis

Mean response times (RTs) to probes served as the dependent measure of interest. RT outliers were removed using a recursive procedure with a moving criterion [34]. The remaining mean correct probe RTs were entered into a 2 (probe location age: infant, adult) 62 (probe location race: South Asian, White) 62 (participant race: South Asian, White) analysis of variance (ANOVA).

Pilot Study

A preliminary study was conducted where eight South Asian participants and eight White participants (all female undergrad- uate students) rated the 32 selected stimuli (see Apparatus and Stimuli, below) in terms of pleasantness and arousal. The stimuli were presented amongst 16 additional grayscale images, eight of which were flowers and eight of which were world leaders and politicians (of different races). The different categories of images were scrambled and presented separately on a computer screen using Microsoft PowerPoint. For pleasantness ratings, participants rated how warm they felt towards each image by indicating a particular temperature on a thermometer ranging from 0u (no warm feelings) to 100u (extremely warm feelings). For arousal ratings, participants rated

PLoS ONE | www.plosone.org

4

September 2010 | Volume 5 | Issue 9 | e12509

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