NEW YORK – Why did you splurge on that new pair of shoes? More and more advertisers are trying to tap into the unconscious to divine the invisible forces that drive those spending decisions. Using gadgets to track eye movements, computer maps of faces to capture a momentary grin (approval) or squint (anger), and sensors to measure perspiration or monitor brain activity, companies are mining consumers' raw emotions for information. Ad firms have traditionally measured the success of their campaigns through consumer surveys, but that technique has its limits. "It's not that people won't tell you, they actually can't tell you why they're making the decision they're making," said Jessica Azoulay, vice president of the market intelligence practice at Isobar, a digital marketing agency.