To demonstrate this behavior:

CREATE SCHEMA testA

GO

CREATE SCHEMA testB

GO

CREATE TABLE dbo.Cities (city varchar(50))

GO

CREATE TABLE testA.Cities (city varchar(50))

GO

CREATE TABLE testB.Cities (city varchar(50))

GO

INSERT INTO dbo.Cities VALUES ('Chicago')

INSERT INTO testA.Cities VALUES ('Cairo')

INSERT INTO testB.Cities VALUES ('Atlanta')

GO

CREATE PROCEDURE testB.GetCities

AS

SELECT * FROM Cities

GO

EXEC testB.GetCities

GO

Output is:

Atlanta

...CREATE PROCEDURE testB.GetCities

WITH EXECUTE AS CALLER

...CREATE PROCEDURE testB.GetCities

WITH EXECUTE AS OWNER

These all yielded the same result.